I don't know. I think it's unlikely as Insomniac could become a premier PS3 developer on the same level as Naughty Dog on PS3 while multiplat they will be overshadowed by talented exclusive developers on both sides.
Honestly with R2 they showed that they struggle to make a game in their yearly release cycle with a decent level of polish and get big tech advancements with each game so it would be even harder to get to the front of the pack with multiplat development. Really they need to shape up and get the help from Sony's tech divisions (ICE, SCE Cambridge) to get up to speed with the latest PS3 developments and become the developer they are clearly capable of being.
I have to say, I think you're selling Insomniac short here. For all intents and purposes they are one of Sony's "tech divisions," taking part in all the cross-studio tech sharing that has been of note thus far; with ICE, Guerilla, Naughty Dog, and the other first parties. IMO they are in fact the closest thing to a first party you can have without actually being one (up until now, hypothetically, of course).
The yearly release schedule is, frankly, impressive; half the titles sold across the same employee pool at twice the rate of titles released would IMO be a wash. But obviously the thinking (so far as I would imagine in the context of this rumor) would be the relative ease to port to 360 with what is already a technology platform that lends itself to some abstraction while remaining data centric. I don't know whether this rumor is true or not - and I would like to think not myself - but I would understand either way.
As for "blaming the environment," I mean personally I think it is perfectly legitimate to have pointed out the 60fps dichotomy for example. How would they match games like Uncharted 2, if they are opting to push frames instead of effects? I sympathize with the frustrations.