il explain this yet again lol
xbox 360 is a service thats paid for, as part of that subscription people expect the best online play and good service, microsoft therefore work with the developers of the games and ban people for hacking/glitching etc which ruins the online experience people are paying microsoft for.
they also employ moderators and such with the money from the xbox live subscriptions.
sony in order to compete with the cheaper xbox 360, offer PSN completely free, as its free you cannot demand anything. sony aren't getting paid by you each month, so they really don't care what goes on with us and infinity wards games.
however sony do and will ban if you hack and cheat in their own games, so so long as you don't cheat in a sony developed or distributed game then your fine, which is why no one has been banned for anything mw2 related.
you may also have noticed that they don't read reports either, i've recieved some quite disturbing abuse several times and the reports go completely unanswered despite evidence being provided.
sony won't an for anything to do with call of duty.