SCEA President and CEO, Jack Tretton, wasn't too happy about this either and more on this can be read here
At the end of the story above Tretton goes on to say this little tidbit about what he thinks is going to happen in the future with third party games:
Quote from Jack Tretton
"I think software companies look and say 'there's no check big enough for us to do exclusive development' ...I think it's going to be harder and harder to have third-party exclusives as we move forward."
I think that it's safe to say that FFXIII will have multiply discs mainly because well they are going from Blu-ray to DVD and it takes roughly 3 duel layered DVDs to match 1 single layered Blu-ray disc. So yea there will be multiply discs and really why should it matter whether there are multiply discs or not. The majority of people that will play this on the 360 are the ones that enjoyed Lost Odyssey and Blue Dragon and they don't really care how many discs they come on. Actually the one thing that bothers me about multiply discs is the packaging. Microsoft really messed up the NA packaging of Lost Odyssey by placing the fourth disc in a sleave inside the package; while the Japanese packaging had a really nice 4 disc double wide case which can be seen here.
Also thought that I might point out that Square-Enix won't start working on the Xbox 360 version until they are done with the PS3 version. So basically Xbox owners are getting a port of the PS3 version.
Ok, I'm done and will now crawl back from whence I came.