You all are way too young, is the problem.
Back in the day, we had arcades. Not to be confused with two arcade machines sitting in the bar, actual arcades were entire buildings devoted to arcade machines. And for many of them, "multiplayer" was about getting a higher score. There was no "Frogger" deathmatch, but I could get triple your score and walk away knowing I'd won.
Gamerscore is a callback to those days. A way of boosting your "points" to know you've experienced/mastered more of the game. Now me, I sometimes will go out of my way to get some points if the thing I have to do for it sounds fun (i.e. Get six stars and hold them for five minutes in GTA4). If it sounds stupid (i.e. Little Rocket Man) then I don't bother, but that's just me.
I can see the point of Gamerscore either way, and my play experience isn't really hurt by having them in there.
Also, just as a quick note, I've heard lots and lots of people go on about how XBoxer's compare their completely useless scores in a virtual penis measuring contest. I mean, I hear this complaint ALL THE TIME. Know what I've never, ever heard? The actual contest taking place. Never once have I been in a game and heard someone tell me that their score made them better than me, ever. I'm sure it happens, but to me, the bigger issue seems to be all the bitching about it.
- J