It's odd - the recent Avengers film was the best comic book movie in memory, but there's a big plot hole - no Spiderman. In his home turf's greatest time of need, the web-slinger was nowhere to be seen - despite actually being a member of the Avengers during his career. For those who are interested enough in or knowledgeable enough about the comics, it seems like a gross error, until you learn that what stopped Spiderman from showing up wasn't bad writing - it was two studios owning parts of Marvel's film properties.
Sadly, it's actually due to the legal issues that prevent such a team-up from happening. The Avengers and Spiderman are not, as far as film-making rights go, owned by the same company. The Avengers' film rights are owned by Marvel Studios, while the film rights for Spiderman still lie with Paramount. Frustrating, right? Whether you're a comic fan or a Party Poker player who enjoys the odd Marvel movie, it seems a shame to create such a significant plot hole for the sake of legal/ownership issues.
Unfortunately, such is business, as we'd imagine Marvel are quite happy with their cruising towards $1bn made from the movie. This isn't to imply - and this is an important point - that Spiderman should've been a member, just that he should've turned up to help given that it's traditionally his territory. Once Andrew Garfield shows up as the new Spiderman this year, the Spidey-verse will probably exist seperate to the devastation wreaked by the foes of the forces of good in The Avengers.
It's a complex series of issues, but there seems to be a basic lack of common sense when it comes to planning out a storyline for a comic book movie when people already know that the most famous of Marvel's superheroes lives and works in the place the battle is set, only to not show up. Odd? Yes. Stupid legal departments' fault? Yes.