At the time of your link, there were 7174 votes for Star Wars, today there are 320,631. The sample size is partly what's distorting the numbers and your point. Also at that time, IMDB was mainly used by movie buffs. Who most likely agreed that SW represented a shift in the movie going experience. And that brought out people to the theaters and supported movies as an art form.

Vocally the ESB camp has grown in polls like those, possibly because that's the general populace's opinion. With Star Wars having a fairly universal appeal. But for the fans who liked that universe, Empire is best because it continued the story without diminishing the original, and it also promised more stories. As an entertainment vehicle, the escapism of Empire allowed them to continue being able to separate themselves from normal life for a short time.

With Jedi and the rest of the SW vehicles, providing the rest of the story, and since GL has said that there will be no more theatrical SW movies, the fans have realized it's over and maybe since the ESB time frame represents their high point (the greatest potential for entertainment escapism), that film has aquired the most public appeal.

Because of the 6 film Saga now being the story of Anakin, the camp which only likes Star Wars (ESB's revelation being too much of a coincidence) has more or less bowed out of the debate entirely. Their removal could be another reason behind the increase of ESB over SW.