Although I haven't heard about the specifics, in part it's almost certainly related to the title of Chapter 6: Return of the Jedi. the title for Chapter 6 was originally released as "Revenge of the Jedi." There was even a run of "Revenge of the Jedi" one-sheets (the kind of posters displayed in theater cases). Then, just before the major publicity campaign got underway, it was announced that the [i]real[/i] name of the movie was "[i]Return[/i] of the Jedi." Needless to say, this caused great furor over the "Revenge" posters, which had also been available through the official Star Wars fan club (anyone remember "Bantha Tracks"?), and were shortly selling for $300 and up. When asked why he had changed the name, George Lucas was reported as saying he had to do it that way so the fans wouldn't have a lot of time to figure out what the title meant. (And there had indeed been wide speculation over the "Revenge" title.) So "Revenge of the Sith" seems an obvious sort of title: not particularly revealing but more-or-less fitting, with a strong sonncetion to the other part of the story. Perhaps I should mention that most of what I've seen on the net recently about why "Jedi's" title was changed indicates it was a "mistake." I was a big fan and followed the news at the time, and recall reading the interview with Lucas shortly after ROTJ was released. (As I recall, he wouldn't talk about it until after the premier.)

Maybe...and stop me if I'm wrong, because this is just a stab in the dark...is it because the Sith get Revenge? I'm thinking outside the box here...

because the sith lord darth sidious takes revenge on the jedi