Is able to utilize new hardware improvements as well as dx10
Vista REQUIRES new hardware, but what does it actually do with it? Other than "looking pretty".
The shadows, transparency, and translucency that Vista requires a 2GHz CPU and 256MB graphics card have already been done on Mac OS X 5 years ago with a 500MHz CPU and 16MB graphics card. Sit down and use Mac OS X for about 15 minutes and you will realize what the inspiration was for all of the graphical touches in Vista. Although IMO they are done better in Mac OS X.
Also, everyone mentions DirectX 10. There are already projects out for 1 year now that show that DirectX 10 will run on Windows XP.