I think the 360 sales are going to surprise people. Really. This is America we're talking about. I wouldn't rule out the 360 - especially if the 360 version is on par (no real faults), and Microsoft markets a ton. If it turns out well, I'll be picking it up for the 360 myself.
Tekken is a cherry-picked example. Few people care about that series here. In America, the more mainstream fighting series are Street Fighter, Soul Calibur, or Mortal Kombat, and the 360 has shown better sales in all cases.
Once again, this is about the mainstream. Do not equate Final Fantasy fans with JRPG fans, because that isn't the case. As Kasz has said, Final Fantasy is nothing like normal JRPG's, so the JRPG sales comparisons don't tell us much (not that we have any good comparisons anyway).
It's too early to call, but again, as long as there's no problems with the 360 version, it should not be underestimated. Microsoft will market it, and people will buy it. Don't forget that the 360 version of Resident Evil 5 crushed the PS3's.
