Direct3D10 finally completes the break from the legacy fixed-function pipeline. Developers will use the programmable pipeline to emulate the older, fixed-function steps. Additionally, Microsoft had to rethink its display driver model now that the entire desktop is going 3D. The video card isn't just for games anymore. When you have a 3D desktop and give each application its own 3D window, the display driver has to be flexible and stable enough to handle the video card's increased role in the system. Microsoft split up the display driver to increase stability, to ensure that the 3D desktop stays up in the event that a game or another application crashes due to a graphics error. This change also means that Microsoft will not release DirectX 10 for Windows XP, because many of the Direct3D10 improvements will need the new Windows Vista Display Driver Model.
http://www.gamespot.com/features/6143883/p-4.html
Programs such as games are likely already in the works which will require it.
Cocksuckers.