I wonder why the achievements aren't working on the Giant Bomb page for Dead Rising 2?  Just a glitch in the matrix, maybe?  :/

I don't think they're published on Xbox.com yet?

Is it not out in the US yet?  Maybe that's the problem.  It can out last week in the UK.

They still haven't added the achievements onto Xbox.com for some reason. Once they do they will appear on GB.

I think it goes beyond that though. I just started playing Civ 5 the other day, and the first two achievements I got were updated here on GB, but I've since earned another ten or so achievements and those ones have not updated here yet.
 
Maybe they're working on the whole achievement system, or maybe the system only updates irregularly to scan for your achievements......