Well, just because they're a huge corporation, doesn't mean they're necessarily good at marketing campaigns for everything. Paramount really seemed to get what made the Iron Man movies appealing and built their campaign around making Tony seem cool and funny and basically the guy every other guy wishes he could be. Disney'll certainly have the money to throw around to make Avengers, IM 3, et al. omnipresent leading up to their releases, but you never know if they'll be able to figure out how to market them as effectively as possible.
Granted, these movies have been such consistent hits that maybe just having them all over the place will be enough.