DirectX 11.1 Restricted to Windows 8
Sorry PC gamers, but Microsoft's latest DirectX revision is reserved for the newest OS. Microsoft announced DirectX 11.1 requires Windows 8 and there are "no plans" to back-port it to Windows 7, like how DX11 was added to Vista. One of the improvements DX11.1 brings is native support for stereoscopic 3D instead of having to rely on NVIDIA 3D Vision or AMD HD3D. Gamers haven't rushed to embrace the 3D movement with open arms like some industry members had hoped, so the lack of native stereoscopic 3D may or may not be seen as a loss for Windows 7/Vista users.
DX11.1 also has better support for graphics virtualization, the ability to apply shader-based filters to streaming video, and power conservation provisions for laptop users. If none of those sound entirely compelling to you, well, there's nothing wrong with sticking to Windows 7/Vista for the time being. Maybe if the eventual DirectX 12 requires Windows 8 (or maybe even Windows 9), then there'd be a reason to upgrade.