Slightly OT, but relevant nonetheless:
This may offend younger posters... But the truth of the matter is when you are young (in your pre-teens and teens) you
aren't that sophisticated, or wordly and what you expect out of a film and the reasons you go are vastly different from why someone in their 30s and 40s goes to see a film.
This doesn't mean
every single young person is like this... But there are enough of them on a per capita basis across the country (and the world) on average, for studios to market movies specifically to them because these people DO exist -- And are accounted for via box office and DVD rental demographic breakdown -- Even if every single young person who posts on the internet supposedly "isn't" one of them because they are "too savy" for this kind of marketing
They exist, or marketing research firms and studio PR departments wouldn't go after them with such a passion and spend millions specifically designing and making ads and products (movies; music; TV; etc.) which appeal to this age group more than any other.
Also, another resulting trend from this is appealing specifically to the female part of the teen demographic in particular. Look at how they often have multiple trailers for certian films designed to appeal to either a male viewer (action; fast paced; violence), or a female viewer (slower; romance and relationships emphasized). Hell, the former WB network was built around the teen girl trend of the late '90s with shows like "Dawson's Creek" and "Buffy the Vampire Slayer" after the success of "Titanic" at the box office thanks to teen girls going over and over again.
A more recent example is MTV. This entire network is now the cable equivalent to the WB as almost 90% of their shows are aimed at female teens such as "Room Raiders", "The Real World", "Laguna Beach", "The Hills", "Next", etc, etc -- All of which appeal to teen girls and the things they find entertaining (relationship dramas; dating; etc, etc).
However, even with all of this going on in the background fueling a lot of the decisions being made at the major studios...
The real (resulting) reason there is nothing really appealing at the box office for adults is because whenever the word teen or young person is used, this automatically -- and erroneously -- Is euqated with dumbing down, or over simplifying elements of a story, so this supposed target demographic can understand it better (and hence, recommend it to their friends who will also pay and see it, and so on and so forth).
This is the real problem, point blank.
Studios need to realize that making a movie appeal to a wider-audience does not necessarily mean treat that audience like morons and only cater to a specific portion (teens) of that wider-audience. If they did this, there would be just good films for anyone, regardless of chronological age, in my opinion... But they are a risk averse industry and don't want to take the chance that if they take this risk and it fails, they will look like fools and be out a lot of potential revenue. It's a Catch-22 with currently no real solution in sight.