Well firstly, completing a game's campaign does not necessarily mean getting 1000 out of 1000 achievement points.... Duh!
No, seriously though, Gamasutra's article on the average completion rates for Xbox Live's gamers is actually pretty interesting. Conceptually, the statistics speak volumes about the way we play games in this day and age.
While getting 100% of the possible achievement points is certainly a good way of knowing that you've gotten everything out of your $60 game, does the average gamer consider that "beating" the game? I know that I don't. Why should players force themselves to play the most boring, menial, laborious tasks a game can throw at them, just for the achievement points? I've set myself up for that kind of situation before, notably with last year's Prince of Persia title and Star Wars: The Force Unleashed.
Both of those games were highly enjoyable, but when each glitch achievements on me, I just don't see the point of playing through all over again just because the hardest difficulty wasn't available on the first go around, or because I had to ask Elika to save me too many times.
But enough about me! What about other Xbox Live gamers? As it turns out, the smallish survey group Gamasutra is working with (straight from Microsoft) is "more hardcore" than most Xbox Live gamers and even that group has only 80% of its members having gotten every achievement available for Call of Duty 4: Modern Warfare. Doesn't that make the rest of us not look as bad?
OK, more about me: to put all this gamerscore talk in perspective, I present my overall gamerscore. I have achieved 9880 gamer points, but that's out of a possible 33595 points! Doesn't it seem like a drop in the bucket? Certainly there are plenty of games I haven't finished, or even earned half of the possible achievement points in, but am I a bad gamer?
I'd say no. Looking at the statistics Gamasutra has posted, it turns out I should feel pretty good about my 1000 out of 1000 on CoD4. While over 70% of surveyed players had completed the campaign in CoD4, only about 45% of players had gotten 1000 out of 1000. When all is said and done, gamerscore and achievement points prey on the suffering OCD gamer in us all. I don't think any of us should "feel pretty good" about getting 1000 out of 1000 in anything.