Those came one or more years after Napster, when it was already wildly popular because it was the only tool that did that job.

Like calibre, I guess :)

They all came over a year or two later right?

The Kazaa people then used the same base to create Skype (which was "true" P2P for a long time). I'd say they've done pretty good.

Obligatory: I miss Rdio. That was them too.