Errr, IW aren't providing a network to play on. The network is just a matchmaking service.
There's nothing wrong with that per se, but it shouldn't be the only option for a game like CoD.
Instead of the server admins, you're at the mercy of whichever user happens to click the 'host' button instead of the 'join' button. If they disconnect in a hissy fit because you fragged them, game over. If they've got a shit connection, or their roommate fires up bittorrent, expect big pings as 32 players flood this poor sap's connection past breaking point. Oh, and say goodbye to mods too, and by extension, the next TF2 or Counterstrike.
In short, the convenience you think you're getting in exchange for your freedom and the existence of a gaming community just isn't there at all.