The lack of dedicated server support is the cherry atop the turd cake.
Some people still seem unclear about what exactly it means, so just to clarify, lack of dedicated server support means that players cannot create servers which are separate from the player. ie every game is hosted by one of the players playing, rather than being run on another, stand alone pc. This means that servers are not persistent, and that the game has to pause and migrate if the host drops out. It also means the host has 0 latency and yours is dependent on their connection.
Added to that, it seems you cannot choose which server you would like to join, the game decides that for you. Since you can't set up your own server, you can't choose options, use the console, play on modded servers.. I'm not even sure you can choose maps to play on. Oh, and you're limited to 9v9, maximum. There is no way to increase that. None. Basically you have to play the game the developers want you to play, not the game you would prefer to play. Because they know best. Obviously.
There's no lean, which is a minor thing, but in the context of everything else, significant.
My suspicion is that the PC version is a near direct port of the Xbox version, which by nature uses p2p hosting and denies mods and custom options. The game was rushed for the pc, without having all of the pc specific options added. Now, if Infinity Ward want to develop for the consoles that's their business, I fully agree that it makes far more business sense than developing for the ultra elite pc market where numbers are small and piracy rampant. It would be nice if they simply admitted it though. These changes are not good for a pc fan of CoD, it's stupid to try to pretend they are.
People need to stop comparing Rage to MW2 I think, as far as I can recall, Rage is a small scale, story driven thing more aligned with Borderlands than Modern Warfare. When you have a small number of cooperating players, there's no real need for a dedicated server, but when you're looking for a serious pvp battlefield, MW1 delivered 16v16 and presumably could be persuaded to handle more. Some games in the past have managed hundreds of players on one server and that is when a dedicated box becomes invaluable.
Finally, I will be very interested to see how long it takes for someone to hack decent multiplayer into MW2. It's unreal technology, so in theory innately capable of all the things players are up in arms over losing. If and when that happens we will be in the possibly unique position of having a pirate version of a big name game which is in several serious ways superior to the initial, legitimate release. Way to fight piracy...