It's been a while since Microsoft pulled the ol' 'oh no, this new version of DirectX couldn't possibly work on earlier versions of Windows' scamgasm, but as the relatively friendly age of Windows 7 is overshadowed by the dawning of the firm's desperate desire to make Windows 8 a cross-platform goliath/software shop, an old habit has returned. The next version of DirectX might be a purely iterative one, but if you ever look a game that requires DirectX 11.1 you'll be looking at a game that won't run on Windows 7 or earlier.
While a similar state of affairs with DX10 and Vista raised a lot of hackles at the time, at least in that instance Vista was a pretty significant change from XP, whereas Win 8 is very much Win 7 with coloured square-shaped bits on top, so it's going to be that much harder to swallow any claimed technical reasoning for the ringfencing of DX11.1.
11.1 sounds as though it's predominantly efficiency improvements rather than shiny new features, but a guess that might be enough to ensure a DX11.1 game isn't entirely easily reworked into DX11. But I must bow to the wisdom of the crowds there - if anyone has any smart theories about what 11.1's new stuff actually means for PC games that use it, please do share them below and educate me.
The most obvious addition is native stereoscopic 3D support, which would mean DX11.1 games can do the funny glasses thing on any supporting graphics card rather than requiring separate functionality for NVIDIA and ATI. Given 3D is very much a niche element in PC gaming it doesn't sound like any great loss - but again, the essential issue is whether a game made for DX11.1 will also include a DX11.0 mode. If not, some of us may feel forced into upgrading to an OS we don't necessarily want (and I personally can't stand, on a desktop PC at least) if we want to keep up with all the Shader-Joneses.
The revelation about DX11.1's 8iness came about somewhat obliquely, in the form of an MS staffer claiming it to be so in a tech support thread. "DirectX 11.1 is part of Windows 8, just like DirectX 11 was part of Windows 7. DirectX 11 was made available for Vista, but at this point there is no plan for DirectX 11.1 to be made available on Windows 7." It's not impossible he's wrong, or that MS simply haven't made Win 7 DX 11.1 yet, but it's cause for concern for those of us who are otherwise perfectly happy with snappy, stable, familiar Win 7.