A 580 may be needed for a 64-player map at 2560x1600 w/ all details and aftereffects cranked, but I don't think it's going to be needed to play at 1080P with medium to high details in any aspect of the game. Besides, the Frostbite engine has always been and still is CPU intensive. I think the average gamer is going to max out their CPU before their GPU.
With my GTX 570 and i5 2500K both at stock, I experienced no hiccups in the alpha. Battlefield has always been nicely optimized too.
Don't read into the event, guys. Did you not notice "the way it's meant to be played," one of nVidia's slogans? It's obviously being funded in part by them to not only showcase the game, but do some marketing for nVidia.