Call of Duty: Modern Warfare 3 will support dedicated servers, which Modern Warfare 2 did not (but Treyarch's Black Ops did). The absence of Jason West and Vince Zampella may be part of the reason Infinity Ward will include the open. avoiding the wrath of the PC community by supporting dedicated servers.
In 2009, a West and Zampella-led Infinity Ward caused a fan outcry when they announced there would be no dedicated servers and would instead use a system called "IWNet" that was going to be Modern Warfare's method of weeding out cheaters. Unfortunately, one of the casualties was the ability to quickly find matches.
Console versions could have dedicated servers, but it seems Activision will only allow them on PC, since consoles also work in a closed system.