I can see what you are saying. Tease them with FFXIII and then if they want to play versus they got to buy a ps3 to play it.
As great as that sounds, I do not think it is true. How else would you explain what they did with the other JRPG's SE releases as timed exclusives / exclusives for the 360?
I think it has more to do with money than some conspiracy. After all, how would SE benefit from what you say?
I think FFXIIIVS is a way out for SE to redeem themselves for the cutting they have done in FFXIII. I wouldn't be surprised if SE blame the 360 DVD limitations on FFXIII VS release (although they have already indirectly started doing this).