I think this is already happening in general production of games. Games that are released on both formats are clearly optimised for the 360 because if it were to happen the other way round, the 360 version would be significantly graphically inferior.
Sony always strive to have the most powerful console, but because game production costs are so high nowadays, games companies must make their games multi-format if they want to get a decent financial return, so having a more powerful console is irrelevant in today's market. They need both the PS3 and 360 market, so it's not in their interests to make one version far superior to the other.
Which is all good because I have a strong dislike for Sony's "let's wow everyone with powerful specs" tactics.