"Which software developer wants to adopt a technology that can only be used on the latest operating system?" may be Microsoft's Achilles heel. Microsoft wants to sell the latest version of Windows, but third-party Windows developers want their software to work on all versions of Windows, not just the latest one.
I wonder if more permissive licensing for libraries, allowing them to be redistributed more easily, would have an impact. (This is pure, uninformed speculation.)
MS tried making DirectX 10 a Vista exclusive in order to draw in gamers, but I AFAIK the response was lukewarm at best. I think they could've sped up the adoption with an XP version, but this might've been too difficult to backport.
I was working as a reviewer when DX10 was announced, and I was heavily into the gamer scene at a higher level (actually talking with some of the big indie developers, talking with some of the pro-gamers and such). From what I saw the response to DX10 as a Vista exclusive wasn't lukewarm, it was positively insulted.
The situation got even worse when Vista was released and it came out that Vista was actively stopping some games from working, removing the *.exe's as trojans.
IMO MS rushed DX10 onto Vista way too fast, it should have been released when the OS was actually stable for gaming. They didn't appease the hardcore gamers, developers and especially the pro-gamers (who earn their money from games and don't want them screwing up) with the giant fumble start for gaming.
