I too was there at the midnight show of ROTS with my club and we dressed up had fun, but the majority of the fans were Poser fans, just along for the ride, slumming it with the geeks. As soon as the credits started rolling, half the theater empties. Over the weekend the audience was even more indifferent, because we were doing some promotions and giveaways with the the theater, many were uninterested in the prizes, or the giveaways. When we tried to pump up the crowd, the best we got was a lukewarm reception. And this was the Saturday after opening night.
I run into fans all the time, the "Star Wars - Rocks" fans who were not there from the beginninbg, grew up with it and loved it like we do. Poser fans, jumping on a bandwagon who will blindly scarf up the next value meal that Lucas has to offer without a complaint.
In contrast, Serenity which did absolutle nowhere near the business of ROTS, had a wild enthusiastic crowd in the midnight show. And I don't remember ever seeing an entire auditorium sit through the ending credits of any movie. But I don't think a single person got up until the lihghts came on.