http://halo.xbox.com/forums/f/5/t/97...?wa=wsignin1.0
I stopped earning progress towards Campaign Commendations
You can earn up to the Silver level of Campaign Commendations outside of matchmaking. After that, you will need to play Campaign in matchmaking to make any further progress.
And apparently that doesn't even work, according to some guys at HBO.

EDIT: And stop voting for Hemmorage Slayer, you jackasses!