On a side note most of those games above which you have marked DX10 are really DX9c with one or two DX10 effects. Even crysis - the poster child of DX10 - basically looks and runs identically using DX9c (using the ultra high config tweak on XP). Not one of those games is really using the power of DX10.
DirectX 8.1 was ATI only and got picked up, with real benefits, in a few games. Notably, Halo PC and Battlefield 2. (halo looked almost identical to the dx9 mode with dx8.1, but dx8 looked closer to the dx7 path)
Was directx9.0b on the x800 or 9700pro? If it was on the 9700pro, it got major support, otherwise it's only supported in....every source engine game.
As for DX10, most of what it really offers over DX9 requires a ground up development around dx10 hardware, many of which would be unable to truly handle taking full advantage of dx10 anyway.
As for what dx10.1 offers over both dx9 and dx10, are mostly minor tweaks that can be easily implemented without much (or sometimes any) performance loss. There's already more games using dx10.1 than probably ever made use of the other dx side branches.
				
		
			