The Xbox 360 has this mysterious thing call "Achievements", tasks that the developer puts in the game that, when accomplished, add points to a nebulous score (viewable on the internet) that doesn't actually do anything.
For example: If I knock 30 zombies aside with the parasol in Dead Rising, 20 points is added to my Xbox Live screen name's score.
Most people know about this already, and have had enough time to get disillusioned with it. After all, this score doesn't actually do anything but give you a fuzzy feeling in your tummy, and ePenis bragging rights.
Know then, dear listener, that I have found the reason for achievements: Xbox Live Arcade.