Let's assume we ignore the great films - Schindler's List, Shawshank Redemption and that ilk - and instead concentrate on the fantasy/science fiction/"not at all real" genre.
I would say the original Star Wars trilogy was better. 2001 A Space Odyssey was better. The previous Batman film was better (I forget what it's called though - the one when he 'becomes' Batman). ET was better. Short Circuit was better. Hell, even Nemo was better overall.
Don't get me wrong, Black Knight was a good film. But not a great film. The voting is probably skewed by a larger majority of the target audience (geeks, essentially) knowing how to vote on IMDB, and IMDB having a greater popularity as a filmny website than it did just a year or two ago. I don't believe the voting is at all representative at the moment.