The JRPG fanbase is not divided at all, and no, the XB360 doesn't get "everything else" JRPG wise. That title goes to the DS obviously.
But for home consoles, it's not even divided. The outcome of this war MS does againts Sony is just accelerating the demise of the JRPG genre.
And yes, Japan is the main territory for JRPG, that's why, for example, Trusty Bell PS3 is probably for Japan only. If JRPG sold more in other regions than Japan, things like that would never happen. But they're pretty common: lots of JRPG never see a release outside of Japan.
Which is also why non-japan dwelling JRPG fans are happy when the console that gets the most JRPG is not region locked. That would mean DS and PS3. It's the DS right now, so all is good.
PS3 is only 1.5 years old, and XB360 is 2.5 years old. People actually expected the PS3 to get JRPG before it's 1.5 years old ? I know the MS viral marketers are effective against unprepared people, but I'm still baffled when I see their tactic working.
SO4, even if proven to be XB360 exclusive, shouldn't cause so many meltdowns.
Also, I don't understand (actually I do) why some people absolutely want this to be Sony's fault. This is not Sony's fault at all. Complain to SE if you want someone to blame.
Though this isn't needed. If SE made bad decisions, they'll be the most punished.