I could be talking out my arse here, but from my understanding the Xbox 360 uses a framework that is familiar to most developers, whereas the PS3 could be a bit more of a mystery.
that is true, 360 is like developing for pc as xdk and visual studios etc all play nicely together, all being ms of course.
PS3 is a little more awkward to get up and running but its not too bad. I will say that the debug isnt as good as visual studio debugger, but fuck we cant have it all eh? 8)