Spider-Man And Batman Are not in the avengers because they only defended their own city not the whole America!!
Both were ba<x>sed on somewhat biased root names. Bats? Everyone will scream & run if they are close by, yes? Spiders, just plain scary!<br />
I was going to say Superman, but he would just whup everybody's butt. OK, Green Lantern vs. The Silver Surfer!
Because they are too awesome
They both have day jobs.
Batman is owned by DC, which is a different company. Spiderman kind of had his thing going, but I believe he has been involved in the Avengers peripherally or in various offshoots like the New Avengers.