http://www.kitguru.net/components/graphic-cards/faith/crysis-2-being-re-designed-for-gtx580-expect-delays/
http://www.youtube.com/watch?v=oLFVll0P6CI
Long story short: Nvidia paid EA/Crytek $2million so the Crysis 2's DX11 will be basically custom-designed for Nvidia's new GPU. Whether or not AMD cards will even be able to play Crysis 2 in DX11 remains to be seen.
Way to sell out and piss off a lot of your customers and PC fanbase Crytek/EA. :-/