Looking back at the fictional stories that defined the last decade, you might think of things like The Dark Knight, Battlestar Galactica, or failures like Bionic Woman and Speed Racer. Was this the decade we ran out of original ideas?
Okay, that's obviously not completely fair; after all, this last ten years have also seen things like Lost and Twilight winning over new fans, not to mention the end of the Harry Potter book series. But there's no denying that this has been a decade of recycling ideas: James Bond, Batman and Star Trek all got movie reboots (Trek also got a television one, if you count Enterprise), Star Wars gained new life as a TV show, Doctor Who and Battlestar Galactica was reborn to much acclaim, unlike fellow television reboots Bionic Woman, Knight Rider and V. We even have Tron waiting in the wings for next year, along with a new Charlie's Angels TV show. The most successful "new" media franchises were Transformers and Spider-Man - based on ideas that are over two decades old (You could even argue that things like Lost and Twilight are simply mashing up old ideas into relatively new forms; they're definitely standing on the shoulders of giants, at least). So what happened?
It's easy to just say "Well, the geeks are in charge of media now," even if it's not necessarily untrue. But that doesn't explain how they got there, and why they're not making us fall in love with all manner of new things, instead of retreads of old flames (Does Fringe count as new, or just an updated X-Files?). Personally, I think the blame is shared pretty much equally between creators and the audience. For all that we may cry YARM whenever someone talks about their dream to make the ultimate Logan's Run project, it's as much a desire to succeed as creative backwards-looking that's behind it; audiences, for the most part, tend not to support the new in numbers necessary to make it a big success. Look at the most successful movies of the last ten years: Each one is based on a concept that people grew up on.
So, is it simply nostalgia? Perhaps; it's tempting to play armchair psychologist and stroke the chin, commenting on a return to childhood things following the trauma of 9/11, but it doesn't quite fit, because how does that explain the domination of 2000's The Grinch or 1999's Phantom Menace? You can see definite post-9/11 tropes throughout the pop culture that followed (A simpler morality, where good guys always won and could save us from death from above, in many cases; stories of people dealing with increasingly familiar apocalypses in others), but I don't think that the prevalence of reboots was necessarily one of them. It's not laziness, either; some reboots (Battlestar Galactica, for example) put in as much work as any original concept in terms of worldbuilding and creation.
In the end, it may simply be the result of conservatism on everyone's parts: Audiences don't want to spend time or money on something they don't know will entertain them, and studios/creators don't want to spend time or money on something that they don't know will have an audience waiting for it. Movies like District 9 or Moon, web content like Dr. Horrible and the increasing use of comic books as source material for other media back this up, to an extent; the new ideas, and new voices, now have to find new - and cheaper - outlets through which to make themselves known, and become popular and proven enough for the big time. Maybe that'll have happened by the time they've been around long enough to be nostalgic about.