This has been disscused plenty of times already.
The widely circulated conclusion is that the PS3 install base consists of a set of consumers with a very broad range of tastes. While the 360 install base is more focused, ie. there is a larger 'shooter crowd' in the 360 install base.
The 360 also has a much larger install base in NA, where gamers are more likely to make day-one purchases then their European counterparts.
As for internet hype, a few outspoken posters on a website do not correctly represent the views of the average consumer.
QFT; this is pretty much what I figured out myself. Well, I don't consider the day-one purchases that important but the effect exists nevertheless.
Wouldn't MGS4 be a better game for this comparison? It's pretty unfair to take two very hyped games agains the most hyped games of another console and then forget the best-selling, most hyped game of the other console. Yes, the thing won't change even if the numbers do but it does give a better view on the whole case.