But, as a kid of the early 90's and a big grunge fan, I must comment that I am a Republican that really does care for trees . . . especially when they're Screaming!!! : )
I agree that the current trend is lamentable, but at least rockers have a choice when they license their songs to commercials. What I feel enraged about is cheapening masterworks by putting them into contemptible commercials (e.g., the Stars commercial that blasphemes Beethoven's Ninth by replacing the text of the Ode to Joy with "Movies, movies, movies...etc.). It is an abomination. And then sampling Tchaikovsky's Pathetique Symphony for some car commercial.
They of course use these practices because there is no copyright, which is why there are in need of protection. It's also stifling to today's composers--commercials would be a good way for them to have their music heard. One would hope that new creative output would be encouraged--but no. The same music will continue to be exposed to the public until it becomes commonplace and associated with trite items. Oh, mocking fate! Dulling the sword of genius on the rock of popularity!