A couple of comments after reading this thread...
I'm firmly in the camp of "what's wrong with rock is you grew up".
While I admittedly like stuff from the sixties and seventies, I found rock I liked through the grunge period, and even afterward (primarily Garbage and Bjork, but I'll admit that what's left of my sex drive may have influenced me with both). I've found stuff I like that's even more recent, but I think the fracturing of the audience has a lot to do with the problem of the music. In the sixties it was a lot easier to get exposure to the whole of the form, whereas now it isn't.
I have to admit I'm puzzled by those who hold up Led Zeppelin as an example of great song writing. I'll admit that their novel approach to the blues was intriguing (anyone who was around can surely remember that "WTF are they trying to do???" feeling when their first LP came out), but reworking Willie Dixon, et al. is hardly great writing, is it?