That's 1 game. Look at Call of Duty series for example. They outsell PC version 15-20:1. So the 33% is best case scenario. Also, BF series would have sold even if it didn't have the best graphics simply based on its gameplay. So if BF:BC2 would have sold 33% of total sales, spending $10M extra on even better graphics may only have brought another 5% boost in sales.
Look at almost any other cross-platform games. Call of Duty series, Assassin's Creed series, Dead Space and Mass Effect series, GTAIV, Dragon Age 2, Dirt 2, all NFS series. They look better on the PC but not mind-blowingly better. Sure, the textures are sharper and all (and you get to apply AA/AF), but at the end of the day all of those games are
console ports (because financially it makes the most sense from a developer's point of view). And it will continue to be that way for most games until next generation of consoles elevates the available hardware horsepower. BTW,
Dice has acknowledged in an interview that BF3 will look just as impressive on consoles due to the scalability of the engine. So it's more of a testament to how good Dice's development team is rather than the horsepower of PC hardware available.
If Crysis 1 was originally a cross-platform game, it would have never looked as good as it did. I am 100% certain of that. Because it was developed for the PC from the ground-up, Crytek never had to worry about making the game playable on 7950GT level of hardware. If you really want to push the envelope on the PC, you pretty much have to develop 2 separate sets of art for the game since the consoles simply won't be able to play the game at that level.
You probably know that
GTX480 is ~ 10x faster than a 7900GTX (Xbox360). Yet, PC games don't even look twice as good as cross-platform console games. So clearly, consoles are holding PC graphics back. Crysis 2 is just another example of that. If you look at games like God of War 3 or Killzone series on the consoles, the best looking PC games are not much better. How can that be when we have 10x the graphics horsepower available?