Maybe - just maybe - Criterion wanted to put out the same excellent game on both formats, with gamers secure in the knowledge that a purchase on either console would be money well spent. And maybe that will translate into bigger PS3 sales which will make cross-platform publishers put a bit more effort into their PS3 releases.
The notion that Sony paid them off is somewhat incredible - if so, Sony didn't get their money's worth as the Xbox 360 version is to all intents and purposes identical.
It seems that just about every developer out there is happy to pump out a PS3 cross-platform conversion that is lacking in some respect. Even big releases like The Orange Box or Assassin's Creed are measurably inferior on PS3.
For Criterion to put out a game as technically impressive and as fun to play on both platforms is the way things should be done. I'm guessing they think so too...