I think it's also because of the "community" formula Microsoft is promoting so much. When you pay for Xbox Live you want to play with your friends all the time, my PS3 friends don't talk much about online and a lot of the PS3 exclusives are more single player driven resulting in (imo) players renting more instead of owning. On Xbox most exclusives are multiplayer driven and require Xbox Live so basicaly renting is not the better option.
The other points like more 360 in America and more PS3 in Japan is also a good indicative about why games sell better on 360 than PS3 overall. This generation the bigger games come from the west which are less apealing to japanese people and even then the bigger games from japan are very westernized so they can sell better in the west which 360 dominates.
