Alright guys, I've been seeing on just about every social networking site, blog sites, and right here on CV questioning the same exact thing about The Avengers film:

OMG WHERE ARE SPIDERMAN AND WOLVERINE?! THERE AVENGERS IN THE COMICS! THIS IS BULLSH*T!- A quote taken from one of the Avengers fan-pages on Facebook

So, I'm going to make it very clear on a whole list I've gathered, why this particular crossover did not happen, and why it probably won't happen anytime soon.

Let me begin by saying film rights and comic rights and TV rights are all very different things. In the comics, all those characters (Cap, Wolverine, Spider-Man, etc.) are owned by Marvel Comics. They've been there since forever. That won't ever change. Since Marvel Comics owns them all, every single crossover can and has happened since each character's creation (Namor and the Human Torch, Spider-Man and the Avengers, etc.)

Now the TV rights are another animal. Since Disney bought the TV rights to ALL of Marvel's characters, they can all be used in the same show much in the same way that they are in the comics. So if Hulk wants to team up with Spider-Man in Disney XD's Ultimate Spider-Man cartoon, they can (and have) do (and done) so. Before Disney bought Marvel however, shows like Spectacular Spider-Man and Wolverine and the X-Men were in in their own little worlds, so Spider-Man would've never been able to team up with Hulk back then. Same goes for Wolverine and the Avengers, or Wolverine and Spider-Man for that matter. After Disney bought the rights, both those shows were canceled and now Disney can do whatever they want with them. As far as animated TV films go, I can only assume Disney now has complete control over the characters too, much like Lionsgate did before them (case in point, Wolverine was a main character in Hulk Vs). So, if Disney said that they want to do a Civil War TV movie, I believe they would be allowed to do such a thing.

Edit: It appears that I got some of the TV rights issues wrong. Apparently Chris Yost, the guy partly responsible for Wolverine and the X-Men has confirmed that that particular show was in fact set in the same world as Avengers: Earth's Mightiest Heroes and Hulk Vs. That means that Marvel probably owned the X-Men TV rights all along (which makes more sense now that I think about it. Captain America and Nick Fury had guest appearences on X-Men Evolution when it was on). Also, TV rights are filled with many loopholes, and not every Spider-Man cartoon was owned by Marvel or Sony. My apologies, and thank you @cattlebattle for bringing that to my attention.

Now come the film rights. This is where most people seem to get the most confused. Years ago, Marvel Comics sold many of their characters' film rights to various studios, such as Universal, Fox, and Sony. Because the X-Men and Spider-Man films were so incredibly successful, Marvel Comics decided to open up their own film studio, Marvel Studios. Marvel Studios had recently obtained their film rights to Iron Man, Captain America, and Thor (who were previously owned by Artisan, but they never did anything with them, so Marvel got them back). They also re-obtained Hulk and Namor, who were previously under the Universal Studios name. With these specific characters back under Marvel Studios control, it is possible to not only have an Iron Man movie, but to have Iron Man meet Hulk and Thor in the same film, without anybody getting sued! That's great! Now in 2012, the dream became a reality, and now we have a honest to God Avengers film that doesn't suck.

"Now where do Spider-Man, Wolverine, and Daredevil come in Gambit1024? Why weren't they in the Avengers movie too?" Right here, little voice in my head!

See, Marvel Studios couldn't re-obtain all of their rights. With Spider-Man doing so well at Sony and X-Men doing so well at Fox, neither of those studios would dare give up any of those franchises for anything. If Spider-Man were to ever meet Captain America in the Avengers movie, Marvel/Disney would get the pants sued off of them, because he's Sony's baby. So here's which rights lie where (to my knowledge, anyway):

Sony- Spider-Man and Ghost Rider (and all related villains, characters, etc.)

Fox- X-Men, Daredevil, and the Fantastic Four (and all related villains, characters, etc.)

Marvel Studios/Disney- All the characters that aren't affiliated with Spider-Man, Ghost Rider, X-Men, Daredevil, and the Fantastic Four.

Now of course, there are some little exceptions. For example, the characters Quicksilver and Scarlet Witch were so closely related to both the Avengers (they were both members for a very long time) and to the X-Men (they're Magneto's children), they can be used by both Fox and Marvel/Disney. There are rules to things they can/cannot say, however. In an Avengers movie, they aren't allowed to discuss "mutants" or Magneto or the X-Men. In an X-Men movie, they aren't allowed to discuss the Avengers or Hulk or Iron Man.

"Alright, Gambit1024! I understand why Spider-Man and Wolverine can't be in the Avengers now, after all! But there's still one thing I don't get: Can Marvel/Disney get the rights to those characters back?" They sure can, little voice!

See, the contracts for say, Daredevil and the FF, say that "If Fox doesn't make a movie without these guys in it after this many years, the rights go back to Marvel." Easy squeezie, right? Wrong. Since Fox cares oh so much about the money these potential cash-cows make, (and who can blame them?) they will do everything in their power to keep these names until they realize that people will not pay any more money to see them. That's exactly what happened with the Punisher, and now he's under the Marvel/Disney roof with all of his old friends.

So I hope I've been clear to everyone about this issue, and I hope someone's learned something from this thread. And if you don't wanna read it all, I'll just say it shortly and loudly:

SPIDER-MAN, WOLVERINE, DAREDEVIL AND EVERYTHING ELSE THAT FOX AND SONY OWNS CANNOT BE USED IN A MARVEL/DISNEY MOVIE. IF THEY DO, THEY WILL GET SUED FOR LOTS AND LOTS OF MONEY.

The end. :)

Edit: If you're still not satisfied, @Deadcool provided a very pretty picture to yet again drill heads with this information: