MW3 is basically a 60 dollar DLC pack for MW2 except MW3 will inevitably include it's own over priced DLC map packs that should of been in the original game from the start and multiplayer will be split from MW2 and MW3 now.
I'm probably really wrong on this, but from what i'm seeing, that's pretty much the same thing with any game series that makes games regularly. Pretty much the same stuff with a different storyline, different characters, ect.
Just look at the L4D series. For L4D2, all they did was update the engine graphically, added new stuff (as in guns, characters,) and called it a game. They could have just released that as DLC too. Same with Fallout 3/NV. I don't see anyone complaining about those.
They take the same winning formula, add some minor stuff, slap a new title on it, and BAM a sequel.