This is as bad as the SC2 battle net thing, they really don't give a shit anymore, do they?
LAN allows players to play online matches using pirated copies of games. (Including most of, if not all of, Blizzard's titles using it.) One person buys a copy, lets everyone they know install it as well as a no-CD mod, then use Hamachi or a similar program to play online in the LAN lobby. Several people can play it, with online access (Although limited.). They're allowed to do what they thought best to fight piracy.
OT: Activision's greedy, really. It's a way to charge PC gamers for DLC (Since I'm fairly sure you could just copy the map, rename it and make a few tweaks to turn it into a downloadable 'custom map' otherwise.) and make a bit of extra cash from advertising on IW.net. I don't agree with it, but I was going to get the 360 version anyway, since that's what I used for CoD 4, so it doesn't effect me.
Besides, the console system worked fine. You could still have private games to cater for clans and you could tweak those settings however you wanted. Only problem was that they were hosted off whoever had the best connection. If they were removing mods, I guess they didn't see a need for dedicated servers while using this system.
On the plus side, this means they can have less corrupt leaderboards now.
which, despite drawbacks (ragequitting hosts, etc) it seems to work well enough.
That was one of it's biggest flaws, and they've added host migration so that's pretty much sorted.