Shit you're right. It's been so long since I even touched Call of Duty, that I forgot there is no friendly fire on in that game either. Damn them if that's one of the reasons why it's off. I just figured they got fed up of people complaining about the griefers. But didn't you notice that it was much higher in Reach and Halo 4 than it ever was in Halo 2 or Halo 3? Even the first year of Reach compared to the end.
As for Halo 4, I still remember 4 consecutive matches in a row during launch night where I was getting griefed for weapons/vehicles. It persisted for a while too.
I mean you're always going to run into that with randoms, that's why you don't play with randoms in Halo.