Weezer: Playing Fun Music, Sorta. But really we're paying pale homage to exciting groups like Kiss. Pass the Trader Joe's food, please.Slate started this line of thought and Steve Sailer added quite a few observations to it. You ought to read those if you have time. But I'd like to propose something. Rock seems to be broadly following the same path that Jazz took before it: from fun tied to social drinking and youth  to a period of craft, experimentation and "artiness", to entirely introspective navel gazing associated with coffee or juice with "influences" exercising tyrannical control until the music becomes thin and unlistenable. It is then kept alive by nerdy white people.

  In the 1920's and 1930's jazz was, for the listener, about getting together to dance and drink and socialize. It was fun although ballads could show a measure of grace and beauty in their execution no one confused it with high art. Similarly in the 50's and early 60's Rock occupied itself with girls, surfing and uh... girls.  Songs were praised for tightness and economy and for being fun.

Jazz in the 1950's and 60's especially the be-bop movement made jazz more intellectual. It was time to sit down and listen. You can hardly dance to Thelonious Monk's music but you could appreciate it. Albums like Kind of Blue still sell well today to a certain demographic. Rock in the late 60's and 70's also began experimenting with long formats. The Beach Boys and Beatles were the first to expand the musical vocabulary of Rock and pop in this time. Roughly for the next twenty years rock simultaneously experimented with itself and returned to its country and blues roots. But most of these "back to the basics" movements produced diminishing returns in the "fun". By the mid 1980's rock had mostly lost its rebellious spirit. Nirvana in the early 90's may have been the last band of rebellion that rode a wave of Zeitgeist. Simultaneous to the Grunge movement post-punk bands like U2 were going on self-conscious experiments.

The third stage of Jazz saw much more radical experimentation: Acid Jazz, Fusion. Players like Miles Davis literally turned their backs on the audience and instead played for themselves and the increasing number of music consumers that I can only call "archivists" or connoisseurs.  While Jazz has seen minor kitsch revivals - due in large part to fashion trends and marketing departments, jazz is now mostly bought by old white men, nerds (mostly white) and music students (mostly nerds and white). It is often played in juice bars. 

Increasingly indie rock and indie rock criticism is doing to Rock what acid jazz did to jazz - severing it entirely from a popular audience. That is - separating it from social alcohol drinking and pretending that the only way to understand it is with encyclopedic and even esoteric knowledge of popular music in the last 50 years. Pitchfork Media contributors regularly turn in thousands of words on the most abstruse topics. They parse genres with Jesuitical precision.  The popular kid group at your local high school simply won't do that kind of work to enjoy music. They want to dance and drink (when they get to college-wink). Therefore rock will increasingly have a smaller appeal. Even though I find Franz Ferdinand to be a fun band. It is fun mixed with nostalgia. It is the new New Wave - but its focus it thinner and more intense than the original new wave.

Hip hop artists and critics do not yet demand that kind of scholarship for enjoying hip hop. Whenever fidelity to genres and certain sounds get in the way - something still comes along and blows it out of the water before the entire Hip Hop world succumbs to introspection. Gangsta rap developed east and West Coast sounds centered around certain producers. The moment before it became tiresome - rappers like Outkast and producers like Missy Elliot brought the fun back. But I've seen indie rap acts like the Portland Maine based, white, vegan Sage Francis. I've noticed his appeal to white, slightly nerdy kids like myself. So you've heard it here: nerds will take over and destroy hip hop as well.

A related note on hip hop: 

I think Steve Sailer is also onto something when he describes hip hop as a modern minstrel show. Where old minstrel shows had blacks eating watermelons and "cooning" with absurd and dumb grins on their face the new minstrel shows give us blacks pimping, and shoving guns in each other's faces for gigantic and well paying white audiences. Perhaps hip hop will continue to develop the strains of itself that idealize the entrepreneurial spirit and separate that spirit from drug dealing and gangsterism. In fifty years we will denounce as rascist the hip hop promoted by NWA. "See how even the corporations and record companies and co-opt the black panther movement to sell records to whites." There will be debates about P. Diddy and whether his promotion of the Notorious B.I.G. besmirches his record of promoting a healthier "go- get' em" hip hop for social climbing. Bourgeois hip-hop anyone?