I will agree that there is a right and a wrong way to be doing the DLC - Gearbox software have got it spot on with Borderlands (btw I still need to purchase the last 2 DLCs for that...), and everyone else seems to just treat it as a way to make extra money without really putting thought into what they are charging for. Bioshock 2 is another way of doing the DLC entirely wrongly - the first DLC for that is on the initial install, and all you're paying for is an unlock code!
I don't think that Cinema analogy sticks though - I'd put it more akin to paying the intial cost for the movie then having to purchase your drink from the food vendor there at a wildly inflated price compared to what you get elsewhere.
Also, why do you feel that such content should be free? Again I ask, why do you feel entitled to further content other than what you initially paid for (which, if you do your research, you will know what you get) for free?
Why are developers suddenly public enemy number 1 for wanting to make money? Why should I spend all my time working on something that is not going to provide me any returns?
In this particular case (AvP) I don't play the game so cannot comment on it directly, but the general way things are going now, this is how it's going to work: you pay upfront your inital money, then to enhance the experience you will buy lots of little bits of DLC, which will allow you to pick and choose how you want your gaming experience to evolve. It could also be seen as an anti-piracy measure of sorts (though we then get into the argument of making something that people want to pay for in the first place).
Also there is a difference between a DLC and an Expansion pack, and though that line is perhaps starting to blur, at least for the moment, I still see it as there for now - I would not consider TFT or Brood war to be DLC in the slightest, for instance.