Apparently MW3 on PC will not have dedicated servers Which in my mind is absolutely fantastic. Call of Duty is a game where people feel the need to bitch about everything. So when you give people control over the server rules, they proceed to make everything incredibly lame.
"Umm excuse me, this is a crouch only server. I'll kick you if you stand up again!" (Seriously, people try and balance the game on PC by making everyone do nothing but crouch walk, there are dozens of servers like this.) or you find a server where they ban noobtubes, or last stand, or the Famas, or Ghost, or something equally stupid. Add to that, hundreds of 24/7 Nuketown servers and Admins that will kick you for getting a better score then them and it makes it all a seriously pissy experience.
Dedicated servers are meant for slower games, Battlefield needs them because when your going to be playing the same round for half an hour or so. You want to have a consistent experience. But in COD, the round will last maybe 10 minutes at most. Having a matchmaking system works for that length of game because if the host changes and theres more lag, you'll only have to deal with it for a fraction of the time. It also makes jumping in and out of a game so much easier, just hit a button and play, rather than spend time finding a low ping server and then hoping it doesn't crash.
Dedicated servers are great in alot of games, but not Call of Duty. (At least not the Call of Duty we know today.)