Regarding the "best sci-fi movie ever" poll:

Polls have a notorious bias towards the recent. I remember being told of a poll for best song ever that "Kung Fu Fighting" one- said poll being taken while that song was a big hit. 2001 is number 8? Yeah. I suppose the result does say something about the strength of the Firefly fandom, but I wouldn't be overly impressed even if the fans didn't cheat the poll so blatantly.

I don't think Star Wars should ever be included in a list of best sci-fi movies, though. I love the original trilogy (the prequels had their moments, but overall they were a huge let-down, but that's another argument altogether), but it is not science fiction. Clearly, Lucas and others weren't concerned about making plausible science fiction. They weren't telling a story about the future of human evolution or warning us of the dangerous path we were on. Star Wars is a romantic space opera. It's about exciting stories and characters that draw you in and make you forget the world. It has no connection to reality and does not attempt to seem like a plausible story. It exists in its own world with its own rules. That makes it more fantasy than science fiction. That's not an insult by any means. I just think they're comparing apples to oranges.