The way I see it, yeah, they're stupid and pointless. However, I find them useful for squeezing more out of a game. I mean, I already paid $60 for it, might as well make an attempt at the achievements.
Also, I only bother trying to get all of the achievements on games that deserve that much of my time. I will try for XCOM, but I don't know how likely it is that I'll beat a Classic Ironman game or Impossible at all. I guess we'll see.