Well, Username, achievements for some games are the purpose of those games, just like "reach a score" or "complete a game". A good example is Left 4 Dead. What's the point of L4D, without achievements? It doesn't have a campaign, as such, it has achievements instead.
Also, a lot of people don't try to get achievements to get a score or get a star, they do them because they are fun, challenging, and in some ways a competitive sport.
I don't get anything for unlocking PC's Left 4 Dead achievements, for instance, but I do them anyway because they are a challenge and pretty much the purpose of the game, as you put it. They motivate and encourage me to do things that I wouldn't normally do because they are a part of the game, just like completing a campaign is in most games. You will find people who don't see it that way and do it just for the score, of course, but that's their business. All I know is I have fun with them.
You are generalizing because some people on some website you happen to dig up, are obsessing about achievements. Not everyone who enjoys them, thinks that way.
Also, cool it with the personal attacks, bud. You don't know me so keep this subject neutral and just make your points without putting me in any categories.