But that's my point, you pay $50 (or whatever it is) for the full game. (Which is mainly a purchase of the license, but also includes the disc, case, packing, transport etc.) You should be able to expect at least a fifth (well, a third, since I think that's about how much they get sold to the stores for) of the content of the full game in the DLC, right?
Of course, you don't get it in the DLC because it's much easier to make quick and cheap things and throw them out at premium prices than actually make decent content packs.
If each DLC WAS like a mini-expansion, I wouldn't mind, but they're more like a single zone (or equivalent) and a bit of easily scripted content.