ProggleRock
CAGiversary!
If you complete and game and earn all of the achievements (thus granting you a little icon showing you've completed all the achievements for that game), when a DLC comes out and adds achievements, does the icon disappear? Personally I'm not much of an achievement hunter, but I can imagine this pissing off completionists who like to fully complete as many games as possible only to find out their list keeps shrinking as more achievements are added (that require purchasing).