I hope you're talking about something other than the Alpha, because those numbers don't mean much.
So you're anticipating that the final product will have worse performance than the current alpha? Interesting. Performance will only go up between now and release, and its ridiculous to think that a single high end GPU (ergo 6970 or gtx 570/580) won't be able to play the game fluidly. So i'll repeat: A high end video card will play BF3 at HQ settings, 1080p, just fine.
If you want ultra quality with SSAA, yes, I don't know of any card on the planet that can run a dx11 game with SSAA/16X AF with a good framerate. The GTX 580 can't run Super Sample AA - 16X AF with uber sampling in witcher 2 at a good framerate, and neither can the 6970. If you want Ultra SS-AA / Ultra AF you need sli or crossfire. That applies to any DX11 game, not just bf3.
I'm in disbelief that anyone would think a game would be designed solely for people with SLI or crossfire. With 700$ video card setups. I'm sure that would sell REALLY well

Basically, the ultra setting is just DICE throwing a bone to users of multi GPU systems...but its by no means required for a good experience. Most eveyrone else will fall back on the high quality setting.