I say this not because I'm a Star Wars true believer who will brook no dissent from the Jedi Way. Heck, I'm probably a bigger Star Trek fan if I'm honest with myself. I say this because I'm not sure pop culture works the same way in 2011 as it did in 1977. Certainly there are still fads (and their brain-damaged cousins memes) today, as there were 34 years ago (!), but they don't seem to have much staying power. Paradoxically, I think the ubiquity of cheap, instantaneous, worldwide communication ensures that fads burn out more quickly than they did in the benighted days of my youth when you couldn't pop onto a movie discussion site or forum and find out everything you wanted to know about an upcoming movie. Nor could you expect to see a movie anywhere except in a theater, where any moderately successful film could be expected to be shown for many months rather than mere weeks (or so it seemed to me anyway).
But I think the main factor that prevents most contenders for "this generation's Star Wars" from any plausibility is the way Star Wars changed the cultural landscape forever. Much like D&D, it's not so much that Star Wars burst fully-formed from the head of George Lucas with no cultural antecedents; it's that it brought together a number of things we had seen before in a way that no one else had ever done -- and it fed a hunger that no one knew the popular culture had. Star Wars made science fiction cool and fun and, most important of all, mainstream. Everyone seemed to be a Star Wars fan back then, not just kids and nerds. It was OK as a "serious" adult to admit you liked Star Wars and with that admission came a kind of respectability that allowed these movies and their ideas to take root in unexpected places within the wider culture.
Indeed, I would argue that Star Wars was so successful that it all but precluded the possibility of there ever being a "this generation's Star Wars." There very fact that we still, more than three decades later, talk about Star Wars and use it as a yardstick to measure pop cultural influence is a good indicator of just how potent a force (no pun intended) it remains. There are vast swaths of the population who were born after the release of the original films who still feel as strong a connection as I do, who saw Star Wars on the weekend of its premier in Baltimore in 1977 with my sci-fi-loving aunt. I'm certainly open to the possibility, but will kids not yet born feel the same connection to Harry Potter decades hence that many feel today for Star Wars?
as I have argued before, D&D isn't particularly culturally relevant anymore (though its ideas are), while Star Wars remains broadly appealing and influential. I doubt my children would have even heard of Dungeons & Dragons if I weren't their father, whereas I am certain they'd have heard of Star Wars. World of Warcraft has usurped the Throne of Generic Pop Cultural Fantasy Referent, while Star Wars is still the science fiction referent of choice, even amongst those not particularly knowledgeable about it.
I'm neither a sociologist nor a cultural historian; I'm just a guy who remembers the 70s. So, I can't explain either why Star Wars has remained so vital nearly 35 years after its initial release or why nearly every contender for its place in the hearts of "this generation" has been anything but. However, there's definitely something at work here and my guess is that it has a lot to do with when Star Wars was released. I suspect that, had it comes out a few years earlier or a few years later, it might not have had the traction it acquired. Figuring out why that is so and why no one has ever repeated its level of success would be a fascinating exercise.