There have been several "retro" music movements (big band, early rock) amoung teens lately. The only explination is that the current music aimed at the youth market stinks, and a lot of youth are looking for something better.
Plus, I don't know any baby-boomers that listen to the current releases. They have either gone over to country-rock, or listen to oldies rock. Heck, there are probably more oldies rock stations (cocentrating on the '70s and '80s with some '60s and 90s thrown in) in my town than their are stations playing the latest releases.
Other reasons:
CDs are too expensive. Period.
People are worried about the economy. When people count pennies, the first thing they stop buying are overprice luxaries like music CDs.