The aggregate [gamer] score is precisely what keeps owners of both systems buying the 360 version whenever there is the dual platform choice. I wonder if Micro$oft has some patents around Gamerscore which prevent $ony from integrating such a key feature. Without Achievements and Gamerscore I do not think Microsoft would have been able to charge for their service.

But you do not need to pay for their service to have a Gamerscore and get Achievements. I've been saying all along that Trophies should be mandatory. Sony has too many additional features that are optional that never get utilized. No one wants to spend the extra money or dev time to implement them such as in game music, youtube uploading, trophies, screenshots.

I don't pay for Microsoft's service. I use the Silver account, which is free. It still tracks my gamer achievement scores.