There is a price for every D. You go to the store and buy a D for like 15 bucks, so reselling it for more than 20 is criminal. You get one D for free with a game engine, then you buy another D, that's why the top price for two D is 20 bucks. You would think a game with 3 D will be capped at 40, but then you need to add some A to it, so it's OK if a game with 3 D and 3 A costs 80 bucks at retail, A aren't free.