Agreed, Wildcat....100%.
Pacing is, of course, a far greater indicator of a movie's success than just runtime; but when you've got an ensemble movie that's set against an *epic* backdrop of a full-blown alien invasion, then I really don't see how you could pace Avengers to "accurately" tell its story in less than two point five. Especially when --- who was it, Chris Evans? --- has said that there's something huge going on every ten minutes/ten pages.
Thing is, the superhero "genre" is a catch-all, and includes lots of different subgenres. There's superhero films that are epic fantasy, some that are hard sci-fi, some that are supernatural horror, some that are costumed vigilante crime dramas. The "street level" characters do *not* need epic runtimes, and that's where you run into the problem of making a film overly long and bloated, such as Spidey 3 (some haters might even accuse TDK of that). But at the *opposite* end of the spectrum, when you have an *epic* sci-fi/fantasy movie and you try to ram it down audience's throats in less than 2 hours (in some cases just a few minutes over 1.5), you generally wind up with a dismal failure (see Green Lantern and the FF films....those *deserved* longer runtimes for their epic scopes).