I would give more credit for a site without a box art because they simply cannot have an official box art indicating 18+ if the game wasn't rated by PEGI.
Only GTAIV was rated by PEGI (from the GTA series):
http://www.pegi.info/en/index/global_id/505/?searchString=grand+theft+auto
This box art is fake (which doesn't means that the game isn't coming for the PS3).