Put enough work into any game and you can port it to pretty much any system. I'd say it's more that Sony realizes that this and MGS4 are two of it's real system sellers. People will buy a PS3 for FFXIII and Sony wants to lock it in as an exclusive. If Square wanted to just go and start working on a port from the get go you could conceivably see it on the 360 within a period after the PS3 release. If Sony could lock them into a contract for at least a year or two then they get what they want. One of the few games that actually will sell consoles will be there's for a long enough period to make it hurt for the 360. It'd be a smart business move on their part, regardless of what the odds may be that Square will put it on the 360.