I think it comes from what your expecting in a movie, a short story about what occurred after the series or a separate stand along story. Movies like the gundam 00 and endless waltz fit the first definition.
Movies for other series may be a lot stronger and better developed to the point there they can stand alone such as the disappearance of haruhi suzumiya, which while it is after the series you can watch it by itself and understand what is going on.
