DLC is software's version of "(non)value add".
This has been in existence ever since the first car dealership thought up undercoating, ever since mcdonalds realized it could sell you a toy car or a carton of pies with your hamburger. Basically, as long as commerce has existed, there's been the concept of accessories, addons, or in this case, "downloadable content".
DLC, much like any other addon, falls into one of two categories:
2) Not crap
Obviously, if the DLC is crap, no one buys it, and we move on all the happier. You really don't need that trucoat, it turns out.
It seems that most people have a problem with the "legit" DLC. Everyone would love that sweet new song pack, that awesome new armor, the goggles that yes, in fact, do something. So why are these bastard companies screwing us over? By golly, we want our new content and we want it for free! Obviously the solution is simple. Make all the crap DLC cost something, and no one will buy it. Make all the awesome, totally radical DLC free and/or baked into the core product, and everyone is happy!
This seems to be the sentiment of every DLC complainer. The truth of the matter though is, one gamer's trash is another gamer's treasure. It's far more economical to the developers, and really, the gamers too, to sell a "watered down" core product at $40 and tack on a bunch of $5-10 packs that give you specific content. I spent $50 on rock band, that was great. I spent another $8-12 on a few more songs from bands that I really, really, really liked.
If you took all the DLC out there for rock band (Which in this case is effing impossible, as there are TONS of song packs now), you'd be looking at a $200 product, and then EVERYONE who buys the core product is stuck with the the "Harmonica Hero Song Pack 4 Collection", which I'm sure EVERY consumer is interested in.
Yes, some companies like to gouge stupid customers, and some customers are stupid enough to pay $20 for a different coloured cape. At the end of the day - I say let them. People went crazy when blizzard started selling $25 mounts - almost 2 entire months of game time worth of cost for what amounted to recoloured pixels of existing models. People lost their shit. Really - who cares? Is it effecting you if 10, 20, 100,000 other people want to fork over money for silly rewards? Let them have it. At the end of the day, almost all of the games we play are equally silly. If you enjoy something and want to pay for it, then do it. If you don't, don't.