Some people seem to forget something else along with - surprise, surprise - games haven't fluctuated in price all that much: there's a small chance that someone will have an idea well after the game is completed and released. An extra level here, another character there, hell, even something as mundane as a new costume - someone might have gotten that idea one, two, three months after release. Are you really gonna fault the developers for that? If so, then that's pretty fucking petty.
And "too many patches" are a problem only when they ultimately do nothing, i.e. Ninja Gaiden 2. A new patch seems to drop every 3 days, but they only seem to add to the list of problems the game already has.
One last thing: you feel your game is "incomplete"? Stop playing it, either return it or trade it in, and play something that you feel is better worth your time. It's not that difficult - believe me, I've tried. Watch I get attacked...