Jesus Christ...
Just live with it, alright? If someone really really likes a game, but has played it through like 4 times, they're going to pay for any DLC for that game they can get. Myself included. And it's not fair for you to just say 'Oh, it's OK in Game X, but not in Game Y', because if that's how you're going to look at it, then every game's DLC is instantly justifiable, including Modern Warfare 2's new maps. I also read a very interesting post by a fella on this site concerning the origins and creation of DLC, which stated that it tends to be stuff made that was originally taken out of the game because it was full already, or something made while it's going through its last legs of production. I, like alot of other people, find map packs an inferior form of DLC to add-ons, but there are always people who will buy them, for a variety reasons. Yes, a lot of DLC comes at a heavy price, and some is utterly pointless, and in an ideal world, it would be free [provided you had bought the game it was for], but a company is going to do what it wants to make money. If it's that much of a problem for you...
DON'T BUY IT.
What is an absolute travesty, though, is when you are forced to buy DLC in a game [like Halo 3, to a certain extent]. It should always be an extra, an optional part of the game, and it shouldn't literally limit the game you payed for.
Overall, DLC is here to stay, and it will always be popular among fan-bases of games for which DLC is made. You may not agree with various aspects of DLC, such as the pricing and content [and in some cases, I do agree], but from the looks of it, even you yourself have gone out and bought some, and I'm willing to bet that the vast majority of other people here have too.
