Arcade Fire used to be indie rock. Isn't the very definition of Indie Rock those signed to independant labels, and maybe are relatively less known. On that same vein, these bands are not restricted to do what the record label expects out of them, making them more unique, different, and more or less can do exactly what they want without worrying what beat is catchy or if there's a hook in the chorus or whatever. Arcade Fire sold out the same arena Bon Jovi sells out when they come here. But also is a very pop rock controlled by their label, making them another radio friendly band.

Also, synth does not equal indie rock. It probably makes it more pop rock though.