Thousands of animation and advanced physics rendered per second, take into consideration it is 22++ moving objects with it's unique AI at the same time, that's double or triple your average first person shooter / action game.
In action / fps / adventure genre, there's bag of trick to maintain stable frame rate. Particularly draw distance, level of detail and texture compression. Think like you're in a small box, everything is rendered on limited radius, with post-processing effect to mask the lo-fi texture. While in sports genre, you can't quite do the same because everything is projected at the same time.
Sony and Naughty Dog titles, being an in-house production for Sony Computer Entertainment will always better optimized because it is build specifically for PS3. The same can be said for Xbox exclusive as well (Forza, Halo, GoW).
Like i said before, it's not just about graphic fidelity when it comes to processing power and consumption.
More details,
http://www.azillionmonkeys.com/qed/optimize.html