In my opinion exclusives do have their value. Each console has its own fanbase and the developers have to take care of the individual constumer segments. The first party games are often some sort of measure for the third party games, at least when it comes down to reviews...
Maybe Final Fantasy 13 would have gotten better reviews as PS3 exclusive in the US/UK? While it got very good reviews in continental Europe/Japan where WRPGS and the Xbox are considerably weaker saleswise it was heavily critizised in the US/UK. FF13 was maybe simply reviewed with games like Oblivion or WRPGs traits in mind although it followed a totally different approach (like actually telling a compelling story... not only a shallow main quests with hundreds of sidequests. But enough of that. I somehow simply can not enjoy WRPGs and don't want to upset people wo do). What I mean is that a certain game may get different reactions/reviews on the various platforms because it has different exclusive games to be compared with.
Little Big Planet possibly would have been a different game if it were developped for PS3 and Wii in mind, since it would have had to compete with Mario, Kirby or Donkey Kong Country on the Wii... at least in the minds of the reviewers which often have an influence on the public opinion.
So if I assume that developers are trying to get good reviews they might have different views on what average PS3/Xbox360/Wii Gamers want... So the game might be adjusted to the userbase/fanbase as well, not only to the technical/graphical possibilities of a certain console.
