MS has made quite some deals to get exclusive RPG's in Japan, so quite some of the 360 owners in Japan are RPG fans (besides the shooter fans that also owned an xbox).

Now, SE has 2 exclusive RPG's for the 360, why don't they make FF XIII multiplat? They could sell at least 150k extra unit

Another thing. If SE would have released their RPG's on the PS3 at well (at the same time), not only would these RPG's sell more (partially compensating MS' money), the sales of FF XIII on the would be alot higher, as there would be more RPG fans owning a PS3.

A deal with Sony is the most possible answer, but if so, why wasn't Sony willing to secure ww (timed) exclusivity?

because 150k FFXIII sold in japan is not really important. They need to keep it ps3 exclusive in japan to satisfy playstation fans (psp+ps3)

I bet if FFXIII was released on the 360 in Japan.. the world would end.

I believe it's because the 360 port is going to happen parallel to the localization process. As it is, FFXIII comes out in Japan as soon as the PS3 version is ready. There's always the possibility Japanese 360 version later, though- there was one for Agarest Senki, after all, a game that sold basically nothing.

Sony kept it exclusive in Japan because that's the region where the title will push the most hardware.

If we assume Microsoft threw millions of dollars at SE to make it multiplatform, Sony probably did not (wisely), want to enter a pointless bidding war to keep the title exclusive.

Yet why is it exclusive in Japan? Why didn't MS drive home the stake?

We can only speculate. Either Sony outmanoeuvred MS somehow behind the scenes, or they simply opened their own wallet to keep it in that region.

Microsoft felt sorry for Sony.

It would be more important for Sony that the game remained exclusive in Japan as, like Dallinor said, thats the area that will push the most hardware and possibly even the software (since FF games always have an opening of ~1.8-2.0 million)

It is a shame that the game is not completely exclusive to the PS3 as it would be better for Sony if it had remained that way... Oh well, it is a better thing for Square-Enix though as it maximizes the sales of the game! At least FFXIII Versus is still exclusive (for now at least)

Why would releasing FFXII multiplat, not satisfy PS fans?  Why would they care?

It most likely has to do with localization costs.

I think it's in Square's best interest, in Japan, to make XIII multiplat.

Why? They already have a litany of JRPGs on the X360 already, and coming - TLR, IU and SO4 is coming. If XIII was there, they would improve sales of the 3 titles, as users look into the X360's back catalog of JRPGs. That's compared to the Playstation 3 which has absolutely no Square-Enix JRPGs as of yet.

Most likely something along those lines, but people will fail to recognize this. Also, I bet we're going to hear alot of changes regarding FFXIII in the near future. Not sure exactly what, but yeah.