My best guess would be that the average age of PS3 owners is higher than that of 360 owners. Not because of the preferences over systems themselves, but because of the price. Most parents don't want to buy their child a PS3 when a 360 can play most of the same games and the price for the arcade is half of the PS3. This is what fueled the 360s lead in the US. Once a million or so teens get their hands on a 360, it becomes a fad.
The PS3s price at release was just way too high for most parents to buy one for their child. My best guess would be that a lot of the PS2 fans that were a little older in age bought their own PS3 out of loyalty. It just hasn't had the price until the slim to attract a whole lot of younger players. That combined with the fury that the Wii unleashed upon most children and families when it released meant that most children were completely satisfied with the gaming system they had and didn't feel the need for a PS3 and parents never felt the need to buy one for them.
If the PS3 had a much lower price point at release, things may have been a lot different this generation. It may have been the 360 with the largest mature audience or some other side-effect.
This is all just a theory though, but it fits nicely into the situation. Most kids don't get online to argue about statistics and have a firm grasp on common sense or reasoning. It really doesn't have much to do with the systems themselves, but the prices that have caused them to attract different audiences.
