Many (most) people really lock into 'their' music...and that's usually the music that was popular with themselves and their peers at about the time they hit puberty, high school, etc. At least two things come out of this...the youth/younger generation is into music that drives the older generation up the wall (if for no other reason than it is different) and, the younger generation eventually ages but holds on to and looks favorably back to that music they loved.

I think that might be why we saw such a surge of oldies (50's - 70's) radio stations the past couple decades. The boomer generation not only still held dear their music but they were now one of the largest and most affluent demographic groups in the country. In turn, the oldies stations were followed by 80's and 90's stations and so it goes.

All of this might be at its end. With all the sub-genres of music, and sub-genres of sub-genres, it's hard for me to see the continuation of the same kind of patterns with the same broad coverage. Maybe certain sub-genres will become the new oldies...