This fact is as much down to Media Molecule's platform focus as it is the unique selling points of the PlayStation 3. "With LBP as it is," Evans explained, "We couldn't have made it on the Xbox 360 and the reason for that is actually because we designed it around the PS3's strengths."
"In other words, if you're a game designer, from day one you know your platform, and you just cane it on that platform," he went on. "You're not worrying about cross-platform, you're not worrying about anyone else's hardware design."
Evans cited the inclusion of a hard drive with all PlayStation 3 models as a crucial factor. "If we didn't have a hard drive on every unit, we'd have to scale back the ambition of what you could save and do."
He was careful however not to appear critical of Microsoft's console. “The 360 is an incredibly capable machine, and you could make a user-generated content game on it, no question - just as you could make one on the PS2 or the Megadrive, or any platform. But because we picked our platform, you go and you use every available bit of space, every little processor cycle.”
LittleBigPlanet is out in October on both sides of the Atlantic, where it joins a sparkling list of PS3 exclusives. More info as we get it.
So yeah, LBP was built from the ground up for the PS3 (duh), but the main reason given for it not being able to be on other consoles is other consoles come with too little storage.
This brings up a question I had some time ago which never found an answer: Just how big are user created stages going to be? Is an averaged sized side-scrolling level going to be in the 10's, 100's or 1000's of MB? Obviously it will vary based on content, but would your typical 2-d mario stage be a few hundred megs, or will it approach a gig or more? If it's the latter, I'm afraid downloading user created content will be done on occasion only, and not a big feature.
I can't imagine it'd be much more than 100 MB, as all the storage intensive stuff (models, sound) should already be on anyone's console. I could see where custom textures will inflate the size. Perhaps they will have an initial load of a few gigs like GTA4 or MGS4.