David Bowie's got great music lineup spanning every decade of his career from the 1960s to the day he died. I think people who enjoy his music can easily pick out a definite classic from every decade and everyone has their own favorite period.

Tom Waits started out as an okay musician, and he grew into his own sort of music with age. He's known for his grit and grime, and it's much more profound in his later work than his earliest stuff. A song about being a worn out old drunk on the side of the road hits harder when you hear it from a rugged middle-aged man than a young 20-something.

With these two, Bowie constantly updated his image and tried new things. Tom Waits simply advanced the atmosphere he built up in his earlier work. I think a lot of other popular musicians put more energy and liveliness into their earlier works and can't keep up with it as they get older, or they end up following some music trend that they think will get them pop success instead of just doing their own music.

Virtually every indie band does the latter as they start to get fame, and it often turns off their old fans immensely when they see them become just another soulless pop band.