The Prudential Center isn't really secondary to the Izod Center. That place should just be torn down since more events are being held at the rock. I do agree that it is weird she isn't playing at MSG.
Although it may not seem that way, Izod and MSG are both considered primary markets while the Rock and Nassau are both secondary. I guess once Izod gets torn down, the Rock will be primary and that "new venue" in Xanadu will be secondary. That is, if Xanadu ever gets built lol