Having a few years of copyright protection is a good incentive. But a hundred years? Or seventy years after my death? (If I live to 80, it will become legal to print your own copy of Jennifer Government in 2123.) There's no additional incentive in that. There is nobody, and no company, thinking, "Well, this is a good song, but if I only get to keep all the money it makes for the next 50 years... nah, not worth developing it."Link (Thanks, Sidney!)
Copyright extensions, of the kind popping up everywhere lately, have nothing to do with encouraging more creative work, and everything to do with protecting the revenue streams of media companies that, a few generations ago, had an executive smart enough to sniff out a popular hit. It's a grab for cash at the public's expense. The fact that there is any posthumous copyright protection at all proves that the law is intended to benefit people who are not the original creator: that is, heirs and corporations. The fact that copyright extensions retroactively apply to already-created works proves they're not meant to encourage innovation. The only reason copyright extension laws keep getting passed is because the people and companies that became fabulously rich through someone else's idea are using that wealth to lobby government for more of it.