User blog comment:Damac1214/Black Ops II Patch Notes + Micro-Transactions on the Way/@comment-5952837-20130314033140/@comment-3967954-20130317132229

I think the nerf was probably due to the fact that once you get an LMG, the whole thing just becomes a walk in the park. Obviously they don't want Zombies to be overly-hard, but they're still aiming for it to be a challenge, which is why they're trying to balance everything out slightly.

Having said that, I still don't understand why the wonder weapons have to have a downside now; surely the point of a wonder weapon is that it's deliberatly overpowered?