Why don't superhero films = increased sales?

In the recent mini furore over these two posts (here & here) there was this comment by Dave at Nostalgia:

what I would like, as well as getting more wet liberal Guardian readers (I can call them that because I am one) who've latched onto Persoplis into a comic book store, is to get just a small percentage of the people who go to see Spiderman 3 into the store...and make them buy comics.

I understand the talk of the real mainstream viz a viz Waterstones/Borders ie they sell all kinds of fiction, but to say "the real mainstream is the sorts of things that the general populous enjoys. Hence crime, romance, real life, drama, sci-fi and fantasy are real mainstream but superheroes are not." is a bit disingenuous. As far as popular culture goes it includes lots of superheroes, hence biggest new show on US TV is "Heroes", most eagerly awaited film of the summer is the aforementioned "Spiderman 3".

Fair point.
And one that got me thinking.

Yes, there are an awful lot of superheroes in the popular culture, whether it's films, TV or just in the public perception of things in general (think Only Fools & Horses, the Fathers for Justice campaign, numerous tv ads etc etc).

And the incredible exposure that the characters get from the blockbuster movies and popular culture is quite amazing. But the problem for comics is that these film and pop culture superhero fans are fans of the films and the merchandise alone.
It's always been a problem behind these big blockbuster films. Every time a new franchise comes along, whether it's Batman, Superman, Spider-Man or X-Men there is a small to medium sized sales spike around the film but very quickly we settle back to pre film sales levels for the comics.
Sales of lunch boxes, duvets, action figures et al are generated from the movie's success, but not long term comic sales.

I think this is because we're selling the fans the film experience and everything related to that is seen as mere merchandising for the film, including the original comics.
I'd love to see those bums on seats in cinema converted to footfall through comic shop doors, but it just doesn't seem to happen.

Again, perhaps if a re-education about comics as a medium happens, where comics are seen more and more in the eyes of everyone out there as a valid and worthwhile medium with lots of different things to say it may slowly change.

But again, as Dave has said, the re-education takes a long, long time.
But I think we shouldn't get too dispirited about it. I look back at comics when I first started at Nostalgia & Comics and then look at the comics landscape now. It's an incredible transformation in just 20 years. The rise of the graphic novel as, increasingly, the future of the medium has played an incredible part in this change. The idea that these comics are now things that have a longevity, have a respectable shelf presence and most importantly can be used to tell many different types of story to many different types of people is a wonderful and positive thing.

Hopefully in 20 years time I'll be able to look back and talk some more about all of this and comics will be an accepted, important medium to the real mainstream I was talking about and we'll all, superhero fans, crime fans, sci fi fans, romance fans, humour fans, horror fans, drama fans and every other fan, be visiting Nostalgia & Comics and other great stores to partake in the medium.

But until then, there's a lot of work to be done by us all......