I said:
Perhaps there's another term for this, but I know it as "Trading on Promises." For example: a movie trailer itself is rarely "awesome", but it trades on the promise that the actual movie will be "awesome"- therefore the trailer is "awesome." If that promise is "broken" by the actual movie (by being non-awesome) then the trailer also assumes a non-awesome state.
http://io9.com/5555999/when-a-terrible-movie-has-an-amazing-trailer
Kind of along similar lines.