An interesting note here:
Incredibly, The Avengers‘ 50 percent drop is the smallest second weekend decline of any film that achieved one of the Top 10 opening weekends of all time. Harry Potter and the Deathly Hallows – Part 2 fell by 72 percent after its $169.1 million debut. The Dark Knight dipped 53 percent after its $158.4 million start. The Hunger Games and Spider-Man 3 both sank by 62 percent after their debuts of $152.5 million and $151.1 million, respectively. Those sorts of drops are just expected when dealing with gargantuan openings like these, but Avengersstarted much higher and fell by much less — a clear indicator of positive audience reception.
So in other words, people really like this movie.