Good question and I have no idea... but if you think about it:

These messages going back and forth have nothing to do with the game. If he was yelling profanities at you in the lobby of the game that is one thing... but sending someone a message can happen no matter which game you were playing, or even if you were even playing a game.

The PSN has a player blocking feature. I use it a lot.

Maybe I do have an idea...

When you report a player via the in-game report feature, the report definitely goes to the appropriate parties. The punishment is not automatic and will not happen instantly. These things do take time, but eventually, the abusive parties are caught and punished. Please refer to the "Offensive_Behavior" clause in the Code of Conduct posted on these forums:

http://community.callofduty.com/thread/200386535

Reporting the players through the game, and reporting them to the first party (Sony in this case), would be the right thing to do. Reporting these players helps tremendously.

If he verbally abused you, yes the IW mods can do something about it, but since it was over a psn message, it in no way has any connection to COD, IW or Activision and as such they don't have legal ground in said area.

A few days ago I was watching someone on twitch.tv that was playing on the 360 who kept getting host booted by the same guy, he ended up calling microsoft to complain and see what could be done, the guy from microsoft said that reporting players through your system is almost a waste of time because little to nothing ever happens to the reported player unless they've been reported many many times and that if one person reports a player say 20 times they only really see it as one report because it's only coming from one person and that if anything was to be done to the individual being reported multiple people would need to report the player. So instead of reporting someone a boat load of times send msgs to everyone who was playing with you asking them to report the player also. Hope this helps.