I don't understand this mindset. People who buy things aren't idiots...they buy things because they want them. If it's worth the cost to them, if they have enough free money to buy something that is too expensive for you, how are they getting fooled? Is there an epidemic of DLC that lies about what it includes?
Players do notice and appreciate the work. At least I do, and my friends do. We care about the industry enough to learn about it, and are aware of the work it takes to do a "simple" thing like...putting accurate reflections in a mirror in a game. If a company feels that their DLC is worth less, then they can price it lower, and if they price it too high, then people won't buy it and they're re-price it to match. If it's making a lot of money, it's the right price for a large amount of people.
While I won't say that they're being fooled, I don't think the masses buy DLC because they think its worth it. From what I've seen, most people buy DLC for the content, not for the price. This may sound good, but it really just means that "so long as the price isn't completely outrageous (and by this I mean, say, more than the base game costs), they'll buy it". It's a generalization of course and it obviously isn't true for everyone, but it's not a good thing when price is disregarded. This is the reason why some games can sell Season Passes with...say, a tenth or less than a tenth of the actual content that is included in the entire game for just ten dollars less than the game itself.
There are deals, though, and they work. For instance, I remember Call of Duty Elite, which was $40 more than the base game, saved you $10 that you would have lost buying a Season Pass. And people bought it. The thing is, and I think this definitely holds true with multiplayer games, people feel obligated to buy the content. If a game is popular, or in more cases, if they like the game, the masses will buy the DLC for it. Why? Because it's there. Companies won't reprice their DLC because they never need to, it's hardly ever any skin off their bones if they keep it at the price it is. People will inevitably buy it, and the company will inevitably make money off of it.
Not all gamers are like this though, but I feel that the masses (aka the Mainstream or Core gamer) and the Casual Gamer will look at DLC as "something I have to get" rather than "something I have to pay for". It is new stuff that is advertised to make your game better, regardless of if it's a costume or a new story. The masses are undiscriminating, they are "easy to extort". They aren't stupid, though; they are undiscerning. For the most part. I can almost guarantee that an average gamer will not be a appreciative of the content as you or me, it's just more to play. This may sound "elitist", but I don't think that necessarily makes us better than them, that's just how things are in gaming today. The commercial tactics used in most DLC, regardless of whether it is overpriced or not, is made to make you feel as if your game is incomplete without having all of the DLC. "Your game will be so much better with this!" "Experience the power of this!" "Your game will not be complete without this! "Return to the land of X to take on another exciting adventure!"
Heck, sometimes it's hard for me to stop myself from buying various customization options in games because I feel that my creative abilities aren't what they could be if I did have such and such DLC. If it had never been created, 9 times outta 10, I probably wouldn't have wanted it at all. When I do download it, I might not even use it at all, but it feels good just knowing I have it...right?
That's the sort of obligatory feeling I'm talking about, though that example is fine-tuned for my own interests. At that point, it's hardly about how much I'm paying so much as it is that I'm paying at all. I'm a more frugal gamer, so I'll think long and hard about pretty much any gaming choice (especially DLC), but most people aren't like me. For them, it's a matter of "should I get it or should I not" and "will I be paying up the tailpipe to buy this DLC?"
I personally think that most DLC is overpriced, but it doesn't really matter, people will continue to buy them anyway without so much as a complaint. I like DLC, and there are a bunch of fairly priced DLC items out there, but it many, MANY cases, I've seen overpriced, unnecessary, or just plain ridiculous DLC that calls out your name simply because you have the game. It's a call that's hard to resist, but it is also a call that one will regret when push comes to shove. I really wish people would speak out and say that "$20 dollars is way too much for 2 or 3 maps" or "$10 dollars is too much for a skin pack"...but maybe I'm just in the minority.