Both Naughty Dog and Insomniac had strong franchises on the PS1 (Crash Bandicoot and Spyro) which they left behind when the PS2 came out. What's cool is they replaced them with other strong franchises (Ratchet & Clank and Jak & Daxter). I'm kinda hoping they do the same with the PS3. Ratchet and Clank are great games but I'm much more interested in something new taking advantage of the new systems' capabilities.
Well, Insomniac has already brought us a new IP (Resistance) so it sounds like they are trying a bit of both this time around.
IMO aside from Squenix, Insomniac is Sony's far and away most valuable developer. And I hope they keep Ratchet going-there is no reason not to stick with an IP that has been as consistently fun, funny, and clever.