Rock music today cannot reproduce the excitement of its youth. People who were listening to music in the 60's and 70's remember the excitement, anticipation, and mind-opening of new albums by great rock bands. Progressive rock stations played that music, not corporatized market-oriented pablum. The problem today with "classic rock" is nostalgia. Yes, Led Zeppelin was great, but there cannot be a Led Zeppelin today. To see those old bands on tour is sad and wholly lacking the spirit of rock. For contrast, just look at the films of performances from the 60s and 70s, look at those audiences, and at how intense those concerts were. Not that I begrudge someone making a dollar, but don't ask me to get excited about hearing old songs trotted out 30 years later, or new songs sounding like old songs.
For me, the last interesting, exploratory and challenging rock music was (is) Sonic Youth. The last meaningful rock movement that engaged listeners in a cathartic experience was the Nirvana/Pixies "grunge" scene.
Society underwent convulsions and transformation in the 60's. That is why the music of 1969 is so much farther away from 1949 than 2009 is from 1989. Parents today can listen to the same music as their children. Parents of the baby boom generation had cultural references much closer to their own parents than to their children. Young people in the 60s and 70s had the feeling of being on the crest of a great change. Today there is little originality in popular music. Maybe that's because the concepts and attitudes about life and its problems have remained the same for the past 30 years.
(written as a response to this blog post by Krist Novoselic.)