Fuck Achievements

What's the point of achievements? I've never understood the appeal of these things. Like, I don't own a 360, but even if I did, I don't think I'd get the reason these achievements are worthwhile. At first, I thought you could use the gamer points to buy stuff on Xbox Live, but actually, you cannot. You actually buy stuff on Xbox Live with Microsoft points, which are obtained by paying real money. So gamer points are completely useless. Okay, so if that's not the reason, why are people going after the achievements? Why not simply play the game? Achievements are of course gained through playing the game normally, yet some achievements can only be achieved via ridiculous abnormal behavior. Which doesn't seem all that fun to do, like only using a pistol in Left 4 Dead. If you don't get any real reward for these, it's hard to see why people would do them.