Previous posters pointed to the fact that right now lots of young people dig records that were made before they were born. That generally wasn't the case in the 70's. Musicians in earlier decades had a smaller inventory of background music floating around in their heads. If you started a band 40 years ago the odds that you'd be stumbling on to something you hadn't heard before were way higher. It shows when bands are hitting something that feels new to them... it can also be apparent when a band is rote or trying not to play something that they heard from Yes, Santana, Led Zeppelin, Zappa, B.O.C., The Doors, David Bowie, King Crimson, Thin Lizzy, Kansas, The Who, Alice Cooper, Genesis, Nirvana, Black Sabbath...In any culture you'll find ebb and flow. It doesn't seem like we're in a period where a lot of people are rushing to the dial for that one new song that really crushes them. Value judgments aside, popular music has become(possibly by statistical necessity) more derivative during the last several decades.