both AMD 5xxx and Nvidia GF3xxx will get DX11 but it will make few games with DX11 and then later 2010 it may get more DX11 games to come up
To be honest I would expect a fair amount of games to be made with DX11 over the next 6-9 months.
The reason we haven't seen DX10 games a lot is due to the stigma of Vista. Win 7 is extremely popular and so should DX11 too. We'll have the hardware pretty much on release and games to follow soon.
I think DX11 is a break in developing that people have been anticipating to be honest. It simplifies a lot of stuff over DX9 for example as well as having very nice performance features.