" The xml format for Alien Swarm is different from the other achievement games, so sites such as GB doesn't know how to read them. "
I know Raptr wasn't tracking the game's achievements for quite a while, but they finally got it started to recognize them sometime in the last week or 2. I'm not sure how much work it would be, but it would seem it's doable to get the site to recognize them. "
SteamStats still have the same problem as GB. I don't think Valve should expect every tracker side to change their code just because they wanted to try something new with one game.