I don't buy that it's the reccession, exactly. I can't pretend to know much about the economy, but if adults lack the disposable income than the kids do too. Now, it's possible that adults are being tighter with their own entertainment and keeping to Netflix and Hulu, but handing money over to their offspring so that they can have some fun with Vin Diesel. Certainly, the ongoing success of Monsters Vs Aliens would suggest that a lot of families may hold out going to the theater until it's a film that everyone can see and enjoy.
Personally, I think it's a combination of subject matter, money, and motivation. Over the years, I've watched my relatives become more and more reluctant to go to the movies. They rarely feel that it's worth the trouble or the expense to see just any movie. It has to be an event, or have the stamp of reliability. It doesn't surprise me that Gran Torino had a bigger and splashier run than State of Play or Duplicity, because I know which film my relatives would consider to be the better value, regardless of critical opinion.
Of course, it's not entirely our fault as moviegoers. While studios are quick to point out what we're not watching, only one studio executive was willing to admit that rising production costs make just about any box office result disappointing. If you spend $100 million expecting to make $200 million opening weekend, it's bound to be crushing even if you factor in those worldwide markets and DVD sales.
But hey, that's my take -- and I'm hardly an example of a good moviegoer myself, as I find that I spend so much time writing about movies that I rarely have the time to go see them. Perhaps you readers can shed some light on why you think adults are steering clear of the movies.