Technically speaking, there are a lot of people still using the Win7 RC and leaked RTM.
Arguably those people using them would be more likely to be the ones who buy 5870s first.
Couple that with the Battleforge DX11 patch, and you've already got people playing games in DX11.
From what I've read too, Battleforge sees a 40% increase in performance.
I'm expecting some more games that have DX10.1 paths to receive updates bringing in DX11 features to be honest due to the similarities between 11 and 10.1.
ooh, hopefully. would love to give assassins creed a go. looks sweet and wouldn't mind going through it again.