A huge number of major, and many minor, Marvel characters have been Avengers at one time or another. Actually Hulk & SpiderMan were two of the very earliest.By having that family in the contract Universal has a ton of flexibility.
Spider-Man was most certainly not one of the earliest Avengers, FYI. Spidey wasn't part of the Avengers until the 2000s, and it was a big deal when that happened.
So what does that mean for the cast of Avengers Now if it actually does take off with as much hype they've been giving it.
Won't matter. Everyone on the new team is covered in the contract under the "Families" clause.