Street Fighter IV probably didn't make it because of Capcom or something. Tekken 6 is the next-biggest fighting game in the US. Blazblue CT is horribly imbalanced and dead, with Continuum Shift being more balanced (probably not as much as Guilty Gear though) but only on arcade at the moment. KoF XII is a never-was in the US, and as far as I'm aware is pretty dead elsewhere too.Thanks Firestorm!
I'm personally surprised that fighters such as Tekken 6 are being played, as opposed to Street Fighter, the King of Fighters XII, or even the lesser-known Blazblue (which I've heard is just as balanced as Guilty Gear?)... there again, I could probably make the same argument for Brawl which is ridiculously imbalanced, but is a different type of "fighting" game. It seems the roster of pro players has changed a lot from when I used to be interested in it.