Pretty common, if nothing else to pretend that you hate mainstream.

You've got two camps; the whole "corporate rock sucks" ideology and the "it's cool to hate popular things" state of mind. Especially if their loyalty to a specific genre becomes part of their "persona," they tend to reject anything outside of what's acceptable in their inner circles.

Most will eventually outgrow it though. Can't tell you how many people I know from high school who were proto-goths now get excited about upcoming Def Leppard concerts (or other groups they sure as hell wouldn't have listened to as a teen).