Gabe Newell from Valve said to Heise that he believes Microsoft made a terrible mistake by making DirectX 10 a Windows Vista exclusive:
The latest Steam survey, which prompted Newell's comments, show that only two per cent of Steam gamers have a DX10 graphics card and Vista.
Newell also highlighted the cross-platform problem - the fact that neither the Xbox 360 nor the Playstation 3 use DirectX 10 features. This would limit DX10 support given the financial requirement for console versions of games, he explained.
At this point, it's fair to say that nobody except for Microsoft thinks that bundling DX10 solely with Vista has been a good thing for the PC gaming industry - the general consensus amongst both developers and hardware manufacturers seem to be that it fractures an already-diverse PC gaming market even more, making consoles look even more attractive. One only has to look at Bioshock - the PC version has staggering requirements, barely any image quality upgrade under DX10/Vista, as well as installation issues - whereas the Xbox 360 version plugs in and works. Food for thought.