Microsoft has confirmed that DirectX 11.1 will be exclusive to Windows 8.
DirectX 11.1 is the next release of the 3D graphics API and adds, amongst other things, native stereoscopic 3D support, meaning games developed for it will have to include 3D compatibility.
DirectX 11.1 is part of Windows 8, just like DirectX 11 was part of Windows 7. DirectX 11 was made available for Vista (bing it), but at this point there is no plan for DirectX 11.1 to be made available on Windows 7,” Microsoft's Daniel Moth revealed on the Microsoft Answers forum.
Microsoft previously employed this tactic with DirectX 11, hoping that its DirectX 11 exclusivity would help encourage adoption of the new OS.
However, with Windows 8 already facing hostility amongst some quarters of the press, Microsoft risks an even bigger backlash with this latest decision.
UPDATE: Microsoft has contacted MCV to point out that stereoscopic 3D support will be optional, not mandatory, in games developed for Windows 8.