The question of "Is it Star Wars without Darth Vader or Luke" is a great one when it comes to the Episodic movies. The first six movies have in some way been about Vader. That may be Lucas retconning (it was always about Vader) but the truth is the Skywalker and Vader characters have always been a part of those movies.

If we watch all six films together, it sort of makes sense that its the rise and fall of Darth Vader because that's how Lucas structured them in the end. The OT by itself is about Luke and Vader with the others as side characters. With ep. 7, where does the series go? Isn't the main character (according to Lucas) now gone? Why even have an ep. 7 if the story is done? Both of the main bad guys are done. If you're supposed to watch all the episodes together, won't 7-9 seemed tacked on without one of the villains from ep. 1-6 showing up?

The one thing I think that's missing from Ep. 1 is Vader. I like that film but there is a definite absence there that I think caused people to not think of it as a Star Wars film and I don't think it has to do with Han or Luke missing either. In ep. 2 Vader starts to show up in subtle ways and then in ep. 3 makes his full appearance. I believe the reason people liked ep. 3 the most out of the prequels (meaning casual audiences) is because of Vader. He's that huge of a character. Think of it this way. You can make a good Star Wars story without Vader (KOTR, some EU) but they will always pale to the ones that have Vader in them since he is so crucial to Star Wars itself.