The previous DirectX version was DirectX 11 which is compatible with both Windows Vista and with Windows 7. The differences between DirectX 11 and DirectX 11.1 are not that big (the update is mainly characterized by added native stereoscopic 3D support). Because of this people won’t be rushing to upgrade to Windows 8 anytime soon. But since future DirectX versions will most likely be incompatible with operating systems prior to Windows 8 we expect to see a lot of frustrated gamers switch to Windows 8 in their quest to be able to play the latest games on the market.
Windows 8 adoption rate is currently not that great and the internet is full of mixed reviews. All the latest game titles still work very well with DirectX 11. Microsoft can’t directly force Windows 8 adoption unless it is helped by game developers. If the developers begin using new features found in DirectX 11.1 and future DirectX versions then we could see a lot of people update to Windows 8.