Piracy is not all about getting the latest movie, watching it and then dumping it.
People do make reviews, not only about the quality of the released pirated version of the movie, but also about the quality of the movie in general. Moreover, people are rating the movie, its plot, the actors, their acting -- in short, people tell you if it's worth watching or not.
Same thing stands for audio cd/dvd music, if the songs are crap, you'll find a comment by someone saying just that.
Eventually, if the media in the Internet are freely distributed, they could gather real-time statistics about the success of a movie or album, making it even better in the future.