I completely disagree with your proposition. I would ask you to back up your argument that before the internet the general teenager had high artistic and cultural tastes. In fact, before the internet people's absorption of culture was generally limited to whatever was on the 5 TV channels that evening - mass produced media with the lowest common denominator.
The internet allows all youngsters to make their own mind up about what kind of media they enjoy. This allows them to find their own niches, in a way that simply was not possible before. If you look at the research (Chris Anderson's "The Long Tail" is a good book to start), you'll see very clearly that more and more the younger generation are moving away from mass culture and into niches, where they may express themselves culturally to a far greater extent.