Ok, your post is a little confusing. Why is it S-E's problem to make JRPG's sell on the 360? Final Fantasy doesn't need the 360 to sell but clearly the 360 needs Final Fantasy XIII. You see, the problem is, FFXIII already has 2+yrs development on the PS3 and therefore making the 360 version for simultaneous would cause FFXIII to be delayed into 2010 at the earliest, at which point it will help no JRPG's sell on any system. And if the PS3 version gets a 1yr+ head start on the 360 version then the 360 version would be a waste of time anyway. You see, the US market is not exactly a strong one for JRPG's so these excellent attach ratios of the 360 are meaningless to FFXIII because even the 360's own JRPG's are not freakin selling. FFXIII will receive most of it's sales from Japan and if you think Japan will choose the 360 version over the PS3 version so that future JRPG's can sell on the 360 you are in lala land.
Blue Dragon, Eternal Sonala and now Lost Odyssey shows what happens to JRPG's on the 360.
As for MGS4, I am certain we will see a version sometime fall 09, if not even later, but if you think it will just light up the 360 sale charts after being on the PS3 for over a year I think you are sadly mistaken.
Face facts, these 2 games, unless they receive unprecedented delays are not going to do much on the 360. If these games succeed, they will need to do so on the PS3.