Hmmm, lots of tangents and possible explanations (or theories).
We, as old fogies :), are looking back at music from the 60's, 70's & 80's as good music. I too prefer a lot of old rock. But, we are pretty much cherry picking over 3 decades of music. There was a lot of crap around then too. How many of us bought albums for 1 song? I know there were some bands that were glossed over simply because they didn't get airplay. For example, some of you may have never heard of Trapeze. The point being perhaps there is some good music currently out there that is not mainstream and the masses haven't discovered yet. I recently discovered Zero7 to find they have been around for quite a while.
Then there is the mass consumption of music these days. Disney keeps pumping out formulaic pop tarts to indoctrinate the kids. Those kids think that is good music and carry that ear as they grow older. As others have noted, I too believe there is a 'common ear' and when it is stuffed full of crap it knows no better.
What really scares me is 30 or 40 years from now some moron will be referencing Kanye as some type of musical genius.