It’s interesting how this ties into what I hesitate to call postmodernism. As I understand it (correct me if I’m wrong), postmodernism involves a work of art being aware of its medium or even aware that it is fictional. So the practice of what TV Tropes calls subverting a trope–setting up an expectation based on the accepted conventions of the medium and then denying it–would fall under this.
When Buffy sees the freaky sentient vetriloquist’s dummy, she and us both expect it to be the bad guy who’s killing all the students, because there’s an accepted convention going at least as far back as Dead of Night saying that dummies, especially when they can walk and talk, are scary, evil things.
This is a good way of looking at the magic of Penn and Teller. The first time I ever saw them on TV, they were doing the cups and balls trick with clear glasses so you could see how it worked. The variations they put on the trick, and the speed with which they did it (making it almost impossible to follow) was the entertaining part, not the trick itself.
The same thinking that led to that trick led to the version of cups and balls described in the clip above. Teller saw a magician doing the trick and thought it was just some dumb amateur trying to impress him. He clearly saw the magician steal the balls from the outer cups and put them underneath the middle one, though probably no one else did. When Teller played along and said that there is one ball under each cup, he was surprised to find that he was right. The magician was using Teller’s knowledge of closeup magic to set up expectations and deny them.
I think we as a culture are more aware of the rules of fiction than ever before. The result is that playing every trope completely straight results in something watchable, but unforgivably hokey. Like always resolving a V chord inward to the tonic, for those of you who know music theory. Since we know the secrets behind all the tricks, it’s the job of the modern artist to take our knowledge of those secrets and use it to jerk us around.