I think another thing is that ANH introduced concepts and things like the civil war, rebels, Galactic Empire and DEATH STAR and Princess Leia before the movie even started... but ESB and RotJ don't really. They build upon characters and situations understood from the previous films and just update them a little.

AotC and RotS continue to introduce totally new characters and concepts (Dooku, Grevious, Separatists) in the crawls. Perhaps that is debatable is the CN Clone War cartoons are taken into account... but I think there's still a big part of the audience saying, "Erm..... what?" at those crawls.