Don't you have to pay for a movie to get in and buy the overpriced popped corn? That's some expensive popped corn, especially when you eschew the free refill.
Nope. At the place I usually go to, I tell the ticket seller person that I just want to buy a bucket of corn. He (or she) says, k, then I go buy said corn. Sometimes they even sell the tickets at the concession stand itself.
With that being said, I could probably just walk into a movie after doing that. A ticket taker making minimum wage probably isn't going to try to stop me. But I wouldn't do that.