I don't think the clear divide between Sony first party and PS3 third party will ever close, and there are legitimate reasons for this-- like tech sharing, dedicated programming for one platform, a shitton of money being poured into projects, etc. But there's definitely an element of the PS3 being harder to program for at play here.
But at the same time, we should consider what a lot of devs have said regarding the architectures simply not speaking the same language, resulting in the PS3 being "harder" because it is simply second. If you take that Turok demo, it's obvious that this was not just a "omg ps3 hard," it's obvious that the 360 version was sloppily carried over and then dumbed down to run at a solid (albeit still worse) framerate. And with sales the way they are, you can't really get pissed off at developers for doing this.
You're seeing some publishers get rewarded for good ports-- COD4 on PS3 is definitely at or past 1 mil worldwide, and that's not really something Activision would poopoo. But I can only imagine the effort that went into their port. Ubisoft says they have port costs down to 10% of the total budget...and if their future ports sell as well as AC on PS3 has, then I'm sure they'll be happy to continue that (only moderately substandard) porting. The main point here is that it isn't enough publishers. I wonder what Stranglehold sold on PS3-- not that it sold anything on 360 either.
I think that the idea some magical gap will close without looking at reality-- that is, sales-- is probably pixie dust snorted directly into Kittowny's nose. In terms of "first party" games, I think Sony is definitely holding their own or exceeding Microsoft's first party.