Windows 7 introduces a new set of dll files containing exported functions of many well-known WIN32 APIs. All these filenames begins with 'api-ms-win-core' prefix, followed by the functions category name.
For example, api-ms-win-core-localregistry-l1-1-0.dll contains the exported names for all Registry functions, api-ms-win-core-file-l1-1-0.dll contains the exported names for all file-related functions, api-ms-win-core-localization-l1-1-0.dll contains the exported names for all localization functions, and so on.

If you look deeply into these files, you'll see that all these files are very small, and the functions in them doen't do anything, and simply returns a 'TRUE' value. Just for example, here's the assembly language content of RegDeleteValueW function in api-ms-win-core-localregistry-l1-1-0.dll:

084010CE 33C0                    xor eax, eax
084010D0 40                      inc eax
084010D1 C20800                  ret 0008

Moreover, if we look in the assembly language output of many API functions, we can see that they simply call their corresponding function in one of these api-ms-win-core Dlls. Just for example, RegDeleteValueW in advapi32.dll, simply contains a jump to the RegDeleteValueW in API-MS-Win-Core-LocalRegistry-L1-1-0.dll:

ADVAPI32!RegDeleteValueW:
77C6F301 8BFF                    mov edi, edi
77C6F303 55                      push ebp
77C6F304 8BEC                    mov ebp, esp
77C6F306 5D                      pop ebp
77C6F307 EB05                    jmp 77C6F30E
.
.
.
77C6F30E FF25B414C677            Jmp dword ptr [77C614B4]   <-- [77C614B4] Points the import entry 
of API-MS-Win-Core-LocalRegistry-L1-1-0.RegDeleteValueW

The answer is pretty simple: When Windows loads the dll files, all the import entries of these api-ms-win-core Dlls are replaced with a call to a real function in Windows kernel.
So here's our RegDeleteValueW example again: when loading a program into WinDbg, we can see that the jmp call now points to kernel32!RegDeleteValueW function. That's because during the loading of advapi32.dll, Windows automatically replace the import entry of API-MS-Win-Core-LocalRegistry-L1-1-0.RegDeleteValueW to the function address of RegDeleteValueW in kernel32.

75e5f301 8bff            mov     edi,edi
75e5f303 55              push    ebp
75e5f304 8bec            mov     ebp,esp
75e5f306 5d              pop     ebp
75e5f307 eb05            jmp     ADVAPI32!RegDeleteValueW+0xd (75e5f30e)
.
.
.
75e5f30e ff25b414e575    jmp     dword ptr [ADVAPI32+0x14b4 (75e514b4)] ds:0023:75e514b4=
{kernel32!RegDeleteValueW (758bd5af)}

Another new dll: kernelbase.dll

Effects on existing applications - compatibility issues.

API-MS-Win-Core List

DLL File	Function Names
api-ms-win-core-console-l1-1-0.dll	AllocConsole GetConsoleCP GetConsoleMode GetConsoleOutputCP GetNumberOfConsoleInputEvents PeekConsoleInputA ReadConsoleA ReadConsoleInputA ReadConsoleInputW ReadConsoleW SetConsoleCtrlHandler SetConsoleMode WriteConsoleA WriteConsoleW
api-ms-win-core-datetime-l1-1-0.dll	GetDateFormatA GetDateFormatW GetTimeFormatA GetTimeFormatW
api-ms-win-core-debug-l1-1-0.dll	DebugBreak IsDebuggerPresent OutputDebugStringA OutputDebugStringW
api-ms-win-core-delayload-l1-1-0.dll	DelayLoadFailureHook
api-ms-win-core-errorhandling-l1-1-0.dll	GetErrorMode GetLastError RaiseException SetErrorMode SetLastError SetUnhandledExceptionFilter UnhandledExceptionFilter
api-ms-win-core-fibers-l1-1-0.dll	FlsAlloc FlsFree FlsGetValue FlsSetValue
api-ms-win-core-file-l1-1-0.dll	CompareFileTime CreateDirectoryA CreateDirectoryW CreateFileA CreateFileW DefineDosDeviceW DeleteFileA DeleteFileW DeleteVolumeMountPointW FileTimeToLocalFileTime FileTimeToSystemTime FindClose FindCloseChangeNotification FindFirstChangeNotificationA FindFirstChangeNotificationW FindFirstFileA FindFirstFileExA FindFirstFileExW FindFirstFileW FindFirstVolumeW FindNextChangeNotification FindNextFileA FindNextFileW FindNextVolumeW FindVolumeClose FlushFileBuffers GetDiskFreeSpaceA GetDiskFreeSpaceExA GetDiskFreeSpaceExW GetDiskFreeSpaceW GetDriveTypeA GetDriveTypeW GetFileAttributesA GetFileAttributesExA GetFileAttributesExW GetFileAttributesW GetFileInformationByHandle GetFileSize GetFileSizeEx GetFileTime GetFileType GetFinalPathNameByHandleA GetFinalPathNameByHandleW GetFullPathNameA GetFullPathNameW GetLogicalDrives GetLogicalDriveStringsW GetLongPathNameA GetLongPathNameW GetShortPathNameW GetTempFileNameW GetVolumeInformationByHandleW GetVolumeInformationW GetVolumePathNameW LocalFileTimeToFileTime LockFile LockFileEx QueryDosDeviceW ReadFile ReadFileEx ReadFileScatter RemoveDirectoryA RemoveDirectoryW SetEndOfFile SetFileAttributesA SetFileAttributesW SetFileInformationByHandle SetFilePointer SetFilePointerEx SetFileTime SetFileValidData UnlockFile UnlockFileEx WriteFile WriteFileEx WriteFileGather
api-ms-win-core-handle-l1-1-0.dll	CloseHandle DuplicateHandle GetHandleInformation SetHandleInformation
api-ms-win-core-heap-l1-1-0.dll	GetProcessHeap GetProcessHeaps HeapAlloc HeapCompact HeapCreate HeapDestroy HeapFree HeapLock HeapQueryInformation HeapReAlloc HeapSetInformation HeapSize HeapSummary HeapUnlock HeapValidate HeapWalk
api-ms-win-core-interlocked-l1-1-0.dll	InitializeSListHead InterlockedCompareExchange InterlockedCompareExchange64 InterlockedDecrement InterlockedExchange InterlockedExchangeAdd InterlockedFlushSList InterlockedIncrement InterlockedPopEntrySList InterlockedPushEntrySList InterlockedPushListSList QueryDepthSList
api-ms-win-core-io-l1-1-0.dll	CancelIoEx CreateIoCompletionPort DeviceIoControl GetOverlappedResult GetQueuedCompletionStatus GetQueuedCompletionStatusEx PostQueuedCompletionStatus
api-ms-win-core-libraryloader-l1-1-0.dll	DisableThreadLibraryCalls FindResourceExW FindStringOrdinal FreeLibrary FreeLibraryAndExitThread FreeResource GetModuleFileNameA GetModuleFileNameW GetModuleHandleA GetModuleHandleExA GetModuleHandleExW GetModuleHandleW GetProcAddress LoadLibraryExA LoadLibraryExW LoadResource LoadStringA LoadStringW LockResource SizeofResource
api-ms-win-core-localization-l1-1-0.dll	ConvertDefaultLocale FindNLSString FindNLSStringEx GetACP GetCalendarInfoEx GetCalendarInfoW GetCPFileNameFromRegistry GetCPInfo GetCPInfoExW GetFileMUIInfo GetFileMUIPath GetLocaleInfoEx GetLocaleInfoW GetNLSVersion GetNLSVersionEx GetOEMCP GetProcessPreferredUILanguages GetSystemDefaultLangID GetSystemDefaultLCID GetSystemPreferredUILanguages GetThreadLocale GetThreadPreferredUILanguages GetThreadUILanguage GetUILanguageInfo GetUserDefaultLangID GetUserDefaultLCID GetUserPreferredUILanguages IsNLSDefinedString IsValidCodePage IsValidLanguageGroup IsValidLocale IsValidLocaleName LCMapStringEx LCMapStringW LocaleNameToLCID NlsCheckPolicy NlsEventDataDescCreate NlsGetCacheUpdateCount NlsUpdateLocale NlsUpdateSystemLocale NlsWriteEtwEvent ResolveLocaleName SetCalendarInfoW SetLocaleInfoW SetThreadLocale VerLanguageNameA VerLanguageNameW
api-ms-win-core-localregistry-l1-1-0.dll	RegCloseKey RegCreateKeyExA RegCreateKeyExW RegDeleteKeyExA RegDeleteKeyExW RegDeleteTreeA RegDeleteTreeW RegDeleteValueA RegDeleteValueW RegDisablePredefinedCacheEx RegEnumKeyExA RegEnumKeyExW RegEnumValueA RegEnumValueW RegFlushKey RegGetKeySecurity RegGetValueA RegGetValueW RegLoadKeyA RegLoadKeyW RegLoadMUIStringA RegLoadMUIStringW RegNotifyChangeKeyValue RegOpenCurrentUser RegOpenKeyExA RegOpenKeyExW RegOpenUserClassesRoot RegQueryInfoKeyA RegQueryInfoKeyW RegQueryValueExA RegQueryValueExW RegRestoreKeyA RegRestoreKeyW RegSaveKeyExA RegSaveKeyExW RegSetKeySecurity RegSetValueExA RegSetValueExW RegUnLoadKeyA RegUnLoadKeyW
api-ms-win-core-memory-l1-1-0.dll	CreateFileMappingW FlushViewOfFile MapViewOfFile MapViewOfFileEx OpenFileMappingW ReadProcessMemory UnmapViewOfFile VirtualAlloc VirtualAllocEx VirtualFree VirtualFreeEx VirtualProtect VirtualProtectEx VirtualQuery VirtualQueryEx WriteProcessMemory
api-ms-win-core-misc-l1-1-0.dll	EnumSystemLocalesA FatalAppExitA FatalAppExitW FormatMessageA FormatMessageW GlobalAlloc GlobalFree IsProcessInJob IsWow64Process LCMapStringA LocalAlloc LocalFree LocalLock LocalReAlloc LocalUnlock lstrcmp lstrcmpA lstrcmpi lstrcmpiA lstrcmpiW lstrcmpW lstrcpyn lstrcpynA lstrcpynW lstrlen lstrlenA lstrlenW NeedCurrentDirectoryForExePathA NeedCurrentDirectoryForExePathW PulseEvent SetHandleCount Sleep Wow64DisableWow64FsRedirection Wow64RevertWow64FsRedirection
api-ms-win-core-namedpipe-l1-1-0.dll	ConnectNamedPipe CreateNamedPipeW CreatePipe DisconnectNamedPipe GetNamedPipeAttribute GetNamedPipeClientComputerNameW ImpersonateNamedPipeClient PeekNamedPipe SetNamedPipeHandleState TransactNamedPipe WaitNamedPipeW
api-ms-win-core-processenvironment-l1-1-0.dll	ExpandEnvironmentStringsA ExpandEnvironmentStringsW FreeEnvironmentStringsA FreeEnvironmentStringsW GetCommandLineA GetCommandLineW GetCurrentDirectoryA GetCurrentDirectoryW GetEnvironmentStrings GetEnvironmentStringsA GetEnvironmentStringsW GetEnvironmentVariableA GetEnvironmentVariableW GetStdHandle SearchPathW SetCurrentDirectoryA SetCurrentDirectoryW SetEnvironmentStringsW SetEnvironmentVariableA SetEnvironmentVariableW SetStdHandle SetStdHandleEx
api-ms-win-core-processthreads-l1-1-0.dll	CreateProcessA CreateProcessAsUserW CreateProcessW CreateRemoteThread CreateRemoteThreadEx CreateThread DeleteProcThreadAttributeList ExitProcess ExitThread FlushProcessWriteBuffers GetCurrentProcess GetCurrentProcessId GetCurrentThread GetCurrentThreadId GetExitCodeProcess GetExitCodeThread GetPriorityClass GetProcessId GetProcessIdOfThread GetProcessTimes GetProcessVersion GetStartupInfoW GetThreadId GetThreadPriority GetThreadPriorityBoost InitializeProcThreadAttributeList OpenProcessToken OpenThread OpenThreadToken ProcessIdToSessionId QueryProcessAffinityUpdateMode QueueUserAPC ResumeThread SetPriorityClass SetProcessAffinityUpdateMode SetProcessShutdownParameters SetThreadPriority SetThreadPriorityBoost SetThreadStackGuarantee SetThreadToken SuspendThread SwitchToThread TerminateProcess TerminateThread TlsAlloc TlsFree TlsGetValue TlsSetValue UpdateProcThreadAttribute
api-ms-win-core-profile-l1-1-0.dll	QueryPerformanceCounter QueryPerformanceFrequency
api-ms-win-core-rtlsupport-l1-1-0.dll	RtlCaptureContext RtlCaptureStackBackTrace RtlFillMemory RtlUnwind
api-ms-win-core-string-l1-1-0.dll	CompareStringEx CompareStringOrdinal CompareStringW FoldStringW GetStringTypeExW GetStringTypeW MultiByteToWideChar WideCharToMultiByte
api-ms-win-core-synch-l1-1-0.dll	AcquireSRWLockExclusive AcquireSRWLockShared CancelWaitableTimer CreateEventA CreateEventExA CreateEventExW CreateEventW CreateMutexA CreateMutexExA CreateMutexExW CreateMutexW CreateSemaphoreExW CreateWaitableTimerExW DeleteCriticalSection EnterCriticalSection InitializeCriticalSection InitializeCriticalSectionAndSpinCount InitializeCriticalSectionEx InitializeSRWLock LeaveCriticalSection OpenEventA OpenEventW OpenMutexW OpenProcess OpenSemaphoreW OpenWaitableTimerW ReleaseMutex ReleaseSemaphore ReleaseSRWLockExclusive ReleaseSRWLockShared ResetEvent SetCriticalSectionSpinCount SetEvent SetWaitableTimer SetWaitableTimerEx SleepEx TryAcquireSRWLockExclusive TryAcquireSRWLockShared TryEnterCriticalSection WaitForMultipleObjectsEx WaitForSingleObject WaitForSingleObjectEx
api-ms-win-core-sysinfo-l1-1-0.dll	GetComputerNameExA GetComputerNameExW GetDynamicTimeZoneInformation GetLocalTime GetLogicalProcessorInformation GetLogicalProcessorInformationEx GetSystemDirectoryA GetSystemDirectoryW GetSystemInfo GetSystemTime GetSystemTimeAdjustment GetSystemTimeAsFileTime GetSystemWindowsDirectoryA GetSystemWindowsDirectoryW GetTickCount GetTickCount64 GetTimeZoneInformation GetTimeZoneInformationForYear GetVersion GetVersionExA GetVersionExW GetWindowsDirectoryA GetWindowsDirectoryW GlobalMemoryStatusEx SetLocalTime SystemTimeToFileTime SystemTimeToTzSpecificLocalTime TzSpecificLocalTimeToSystemTime
api-ms-win-core-threadpool-l1-1-0.dll	CallbackMayRunLong CancelThreadpoolIo ChangeTimerQueueTimer CloseThreadpool CloseThreadpoolCleanupGroup CloseThreadpoolCleanupGroupMembers CloseThreadpoolIo CloseThreadpoolTimer CloseThreadpoolWait CloseThreadpoolWork CreateThreadpool CreateThreadpoolCleanupGroup CreateThreadpoolIo CreateThreadpoolTimer CreateThreadpoolWait CreateThreadpoolWork CreateTimerQueue CreateTimerQueueTimer DeleteTimerQueueEx DeleteTimerQueueTimer DisassociateCurrentThreadFromCallback FreeLibraryWhenCallbackReturns IsThreadpoolTimerSet LeaveCriticalSectionWhenCallbackReturns QueryThreadpoolStackInformation RegisterWaitForSingleObjectEx ReleaseMutexWhenCallbackReturns ReleaseSemaphoreWhenCallbackReturns SetEventWhenCallbackReturns SetThreadpoolStackInformation SetThreadpoolThreadMaximum SetThreadpoolThreadMinimum SetThreadpoolTimer SetThreadpoolWait StartThreadpoolIo SubmitThreadpoolWork TrySubmitThreadpoolCallback UnregisterWaitEx WaitForThreadpoolIoCallbacks WaitForThreadpoolTimerCallbacks WaitForThreadpoolWaitCallbacks WaitForThreadpoolWorkCallbacks
api-ms-win-core-util-l1-1-0.dll	Beep DecodePointer DecodeSystemPointer EncodePointer EncodeSystemPointer
api-ms-win-core-xstate-l1-1-0.dll	RtlCopyExtendedContext RtlGetEnabledExtendedFeatures RtlGetExtendedContextLength RtlGetExtendedFeaturesMask RtlInitializeExtendedContext RtlLocateExtendedFeature RtlLocateLegacyContext RtlSetExtendedFeaturesMask
api-ms-win-security-base-l1-1-0.dll	AccessCheck AccessCheckAndAuditAlarmW AccessCheckByType AccessCheckByTypeAndAuditAlarmW AccessCheckByTypeResultList AccessCheckByTypeResultListAndAuditAlarmByHandleW AccessCheckByTypeResultListAndAuditAlarmW AddAccessAllowedAce AddAccessAllowedAceEx AddAccessAllowedObjectAce AddAccessDeniedAce AddAccessDeniedAceEx AddAccessDeniedObjectAce AddAce AddAuditAccessAce AddAuditAccessAceEx AddAuditAccessObjectAce AddMandatoryAce AdjustTokenGroups AdjustTokenPrivileges AllocateAndInitializeSid AllocateLocallyUniqueId AreAllAccessesGranted AreAnyAccessesGranted CheckTokenMembership ConvertToAutoInheritPrivateObjectSecurity CopySid CreatePrivateObjectSecurity CreatePrivateObjectSecurityEx CreatePrivateObjectSecurityWithMultipleInheritance CreateRestrictedToken CreateWellKnownSid DeleteAce DestroyPrivateObjectSecurity DuplicateToken DuplicateTokenEx EqualDomainSid EqualPrefixSid EqualSid FindFirstFreeAce FreeSid GetAce GetAclInformation GetFileSecurityW GetKernelObjectSecurity GetLengthSid GetPrivateObjectSecurity GetSecurityDescriptorControl GetSecurityDescriptorDacl GetSecurityDescriptorGroup GetSecurityDescriptorLength GetSecurityDescriptorOwner GetSecurityDescriptorRMControl GetSecurityDescriptorSacl GetSidIdentifierAuthority GetSidLengthRequired GetSidSubAuthority GetSidSubAuthorityCount GetTokenInformation GetWindowsAccountDomainSid ImpersonateAnonymousToken ImpersonateLoggedOnUser ImpersonateSelf InitializeAcl InitializeSecurityDescriptor InitializeSid IsTokenRestricted IsValidAcl IsValidRelativeSecurityDescriptor IsValidSecurityDescriptor IsValidSid IsWellKnownSid MakeAbsoluteSD MakeAbsoluteSD2 MakeSelfRelativeSD MapGenericMask ObjectCloseAuditAlarmW ObjectDeleteAuditAlarmW ObjectOpenAuditAlarmW ObjectPrivilegeAuditAlarmW PrivilegeCheck PrivilegedServiceAuditAlarmW QuerySecurityAccessMask RevertToSelf SetAclInformation SetFileSecurityW SetKernelObjectSecurity SetPrivateObjectSecurity SetPrivateObjectSecurityEx SetSecurityAccessMask SetSecurityDescriptorControl SetSecurityDescriptorDacl SetSecurityDescriptorGroup SetSecurityDescriptorOwner SetSecurityDescriptorRMControl SetSecurityDescriptorSacl SetTokenInformation
api-ms-win-security-lsalookup-l1-1-0.dll	LookupAccountNameLocalA LookupAccountNameLocalW LookupAccountSidLocalA LookupAccountSidLocalW LsaLookupClose LsaLookupFreeMemory LsaLookupGetDomainInfo LsaLookupManageSidNameMapping LsaLookupOpenLocalPolicy LsaLookupTranslateNames LsaLookupTranslateSids
api-ms-win-security-sddl-l1-1-0.dll	ConvertSecurityDescriptorToStringSecurityDescriptorW ConvertSidToStringSidW ConvertStringSecurityDescriptorToSecurityDescriptorW ConvertStringSidToSidW
api-ms-win-service-core-l1-1-0.dll	RegisterServiceCtrlHandlerExW SetServiceStatus StartServiceCtrlDispatcherW
api-ms-win-service-management-l1-1-0.dll	CloseServiceHandle ControlServiceExW CreateServiceW DeleteService OpenSCManagerW OpenServiceW StartServiceW
api-ms-win-service-management-l2-1-0.dll	ChangeServiceConfig2W ChangeServiceConfigW NotifyServiceStatusChangeW QueryServiceConfig2W QueryServiceConfigW QueryServiceObjectSecurity QueryServiceStatusEx SetServiceObjectSecurity
api-ms-win-service-winsvc-l1-1-0.dll	ChangeServiceConfig2A ChangeServiceConfigA ControlService ControlServiceExA CreateServiceA I_QueryTagInformation I_ScBroadcastServiceControlMessage I_ScIsSecurityProcess I_ScPnPGetServiceName I_ScQueryServiceConfig I_ScRpcBindA I_ScRpcBindW I_ScSendPnPMessage I_ScSendTSMessage I_ScValidatePnPService NotifyServiceStatusChangeA OpenSCManagerA OpenServiceA QueryServiceConfig2A QueryServiceConfigA QueryServiceStatus RegisterServiceCtrlHandlerA RegisterServiceCtrlHandlerExA RegisterServiceCtrlHandlerW StartServiceA StartServiceCtrlDispatcherA