Have they really switched which books are involved in an event? Because as I recall, the last big events at Marvel have ALL involved the Avenger books in some way, or been launched from them. The New Avengers got involved in House of M, they were one of the focal points of Civil War, Mighty Avengers got launched by Civil War, as did the Initiative. All three books got dragged into Secret Invasion, and Dark Avengers was launched by this.
So that's three nearly consecutive events that the Avengers books have been part of or launched from. That hardly seems like switching them up.