Microsoft apparently replaced the Windows Graphic Foundation (WGF) name with the more easier and logical DirectX 10 name as it has supploed developers with official details about the upcoming DirectX 10 API which will be featured by Windows Vista.
The DirectX 10 API will have completely new and faster dynamic link libraries (DLLs) and is supposed to run much faster. The company decided to cut the backward compatibility with DirectX 9, 8, 7 and lower in this API but there will be a way to use games programmed for those APIs. Microsoft will enable support for DX 9 or lower games through a software layer, meaning it might run slower.
The company did this to make the next API faster, it said, and at the same time will take some burden of the CPU runtime. At the same time we learned that DirectX 10 will have support for Shaders beyond Shaders, model 4.0.
Oh and SM4 may even be released before the launch of Windows Vista.