Music Over the Decades

A few days ago I was driving a rental car and listening to the radio. The car was equipped with XM (which is pretty cool by the way), so I had a few hundred channels to choose from. One category which I stayed with was called "Decades." From the 1940s to the 90s, there was a channel devoted to each decade.
I'm not the first one to notice this, but it was very obvious how music has changed over the last 50 to 60 years. In the 40s-60s people like Chuck Berry, Frankie Avalon and the Romantics sang mostly Upbeat, Happy, and Silly songs. Move to the 80s and 90s and I heard singers like Vanilla Ice, Sir Mix-a-Lot, Madonna and Alanis Morisette sing songs which were Edgy, Angry, and Full of Innuendo.
I know there are exceptions, but in listening to the music over the decades, the change is remarkable.