Achievements are a requirement or MS won't let you publish a game for the 360.
Trophies just came out and Sony coudnt force companies far into development of their games to add trophies( because at the time they signed the PS3 licence stating the requirements the trophies didn't exist yet).
My understanding though is that at a given date they will become a requirement so you can expect sometime in 2009 all new PS3 games to support trophies..
Sony can not force developers to patch old games to support trophies though..
The issue for the games coming out right now is that some of them have been golden for a few months and the developers did not want to add trophies afterwards as they would have had to go through another costly round of testing..
PS3-Xbox360 gap : 1.5 millions and going up in PS3 favor !
PS3-Wii gap : 20 millions and going down !
