On Halo 3 you get points for playing? Well, that's new to me. Actually, not 100% new because it's true in the Social playlists, but have you ever played a game in a Ranked playlist? There you get points for winning, which isn't like CoD. Talk about giving awards (ranks, in this case) to anyone but the winners.
Since you know the Halo 2 MM system, i'm quite surprised that you apparently don't know the Ranked playlists of Halo 3..
But that's all i can say on this one. Halo 3 was where i started, so i don't know much about Halo 2's ranking system.