False categories
You know what, this is Grup thing is a totally false category. Rock and Roll in the 50s was an entirely new thing, and anyone older than 30 just was not going to understand it. For better or for worse, rock became a product that has continued to be repackaged and sold to each succeeding generation, and as long as the music is appealing and harkens back to earlier forms, it will sell, and it will sell to young people as well as people who used to be young and into rock music. It's a form of music, like popular jazz, that is universally appealing.
I'm willing to bet, too, that there is a lot more of a generation gap than the people in this article are aware of. Saying "We both can appreciate the same music" is like saying "We both like McDonald's French Fries"--the music they're talking about is marketed to as wide an audience as possible.
This isn't to say that there isn't music out there that isn't driving Grups as crazy as NWA or the Clash drove their parents. Christ, have any of these people heard the crappy metal/punk bands teenage boys listen to these days? They're close to unlistenable. If I could find more than 1 in 10 teenage boys into Death Cab for Cutie, I would be shocked.
But I think the article is pointing toward a real phenomenon of people not really growing up. But I think this is not as common as they think, and may actually be relegated to New York and California. Has this reporter seen the serious-faced government workers schlepping down the street in DC?