Sonic, what you're saying is true. I would kinda rather have them work on different type of game, but then again this way they get to perfect their formula which is not a bad thing either. These are not some crappy teams who will screw it up, which is best evidenced by R&C2 which by all accounts ended up being superior game over it's predecessor despite only one year of development.
ND on the other hand has always released their games on yearly basis and always improved them (talking about Crash here) J&D -> Jak 2 was their first two year development cycle, which resulted in a radically different game.
My point is, both teams are extremely efficient and are not doing anything they haven't been doing regulairly.
For PS3 they will probably come up with something entirely new anyways. It's not like the people are buying their games because of mascot characters they use.