Although that raises the question: hypothetically, of course, would there be any difficulties with incorporating the ASM universe into the Marvel Cinematic Universe? Perhaps the main continuity issue would be the Manhattan skyline, since there was no Stark Tower in ASM and no Oscorp Tower in The Avengers.
Damn, I was hoping that we would not get Spider-man or Wolverine shoved into an Avengers film for at least another 20 years. I had already had enough of Wolverine taking over the X-men movies after X2.
The characters film rights being owned by seperate companies was the only thing stopping that from happening.
I tend to agree about the X-Men. I think the universe is so deep and has its own morals and themes that any other characters would just be a distraction.
Avengers and Spiderman don't need to be as separate, but there's certainly a difference of portrayal. The Avengers are much more public than Spiderman, especially with Tony Stark being openly identified as Iron Man. Spiderman is a more personal story of Peter Parker, which I think will help keep him separate. That being said, Spiderman's involvement with SHIELD was a cool part of the 90s cartoon.
Based on that cartoon, I tend to agree that the ideal world would put Spiderman, Daredevil, and Punisher in one universe, the X-Men in another, and the Avengers in a third.