This is a subject that I find fascinating, because in any society in which there are de facto cultural gate keepers, there will arise subversive strategies to bypass the gate keepers. It is emblematic of our (perhaps hyper-) capitalist society, that the primary gate keeper for music is money. In 2001, before the War on Terror, Salon ran an excellent series on payola and the music industry in the US. Having that as background, you can understand why TV and advertising became such attractive avenues to reach an audience for many independent musicians. As I note in my comment to Kevin's note... TV and TV-advertising has been a significant outlet for techno for a number of years--to the point where there are awards for 'best electronic dance song featured in a television ad'.
I expect with the continuing boom of YouTube, that the internet and word-of-mouth will become ever more important in giving teenagers the music they want to listen to, and in allowing them to claim a cultural identity of their own. And artists and independent labels will continue to find crafty ways to insert their works in out of the way places where they can be found.
Rock and roll died a long time ago. But I expect in the next ten years we will see the beginnings of a new generational form--blending and bending current genres into a new fusion.Somewhat related: WalMart as a cultural gatekeeper.
