So many bitter people in this thread lol.

The reason some games take up so much space on a blu ray disc are two reasons:
1) uncompressed audio
2) repeated data to compensate for slower read times

Uncompressed audio in a game is just a bullet point nothing else. A lossless audio compression will show no difference in quality for even the most expensive home theater system. Go read AVS forum, most people fail a double blind test with high bitrate lossy audio vs lossless so what makes you think uncompressed makes a difference? The PS3 version will probably have better audio but a switch from uncompressed to lossless or more likely lossy for the 360 version will cause a rather significant reduction in size.

Some people are just delusional when they say things like 8-10 discs. It must suck to have to justify your $400-$600 purchase to a bunch of anonymous people. I would say realistically it will be similar to lost odyssey in disc size. Even being a more CGI heavy game I think the programmers at Square are more proficient then those at Mistwalker.

If they don't hold back on the game and make it the best they can then it will possibly fill a 50GB BD (720p, 7.1 sound etc) and when they port it to X360 and localize it to the west then they might compress the audio on the X360 and i wouldn't be surprised if it is a HDD only game aswell, there will most definitely be an install of at least 3GB. I say 4 discs minimum, 6 max.

@HappySquirrel:

Most of the sales for FFXIII will be on PS3 as it is the 3rd gen for a FF to be on a Sony console and the first for it to be on X360, plus they are different types of gamers look at how other JRPG's did on the X360... not too well. It will definitely sell 1million on the X360 but the PS3 version will sell at least 4million (personally i think that is quite a low prediction for the FF of the generation).

This thread is just a metaphor for how certain people feel about the Xbox360 getting FFXIII.

So its not getting intelligent reasoning because of this.