i suggest giving this a read, a great bit of info in there on why DX11 will become a standard.
http://www.bit-tech.net/bits/interviews/2010/01/06/interview-amd-on-game-development-and-dx11/1
specifically
this has to be great news for developers and should make DX11 really help its uptake. You don't need to build a DX11 exclusive game, but if you do build it in DX11 it automatically works on DX10 and DX9 hardware.
So technically speaking no game will ever be DX11-exclusive then as DX11 is the 9 through 11 runtimes rolled together into one package