All of those Marvel films were in heavy rotation for syndication...IM, IM2, Hulk...those flicks are on FX on rotate...Thor and Captain America were two of the most rented films since they've been released for rental.
I don't really buy the idea of reintroducing everyone in such a fashion for movies like this. You don't see Harry Potter 7 reintroducing Harry, Hermione, and Ron for an hour...you don't see Star Wars reintroducing Luke, Leia, and Han again in Return of the Jedi...you don't see Legolas, Sam, and Gandolf being reintroduced in ROTK.
So, I don't buy that excuse, and to be honest, its kind of lazy to do it. Basically, what it says to me, is you didn't have enough ideas to make a 2h30m film with new stuff...you had 1h30m of awesome battling, but you wanted to make it 2h30m, so, you threw in an hour of plot that is being rehashed. I'd rather just see the 1h30m of battle scenes.
Not too dissimilar to Transformers 3, where 1h30m was completely meaningless and boring with the last hour being ridiculous eye candy. Avengers was much better than T3, but same premise of spending a lot of time to discuss stuff that took place over 5 films. So, I either just wasted my time watching five films or I wasted an hour watching the first half of The Avengers. Either way...time was wasted.