Just like Apple let Creative Labs foot the bill on R&D and market building with the Nomad before the iPod was introduced?
But yeah I guess in some way that's true, portable mp3 players of some kind were a rapidly growing market being developed by dozens of companies when the iPod came out. I had an entire series of CD-R/mp3 capable portable CD players back then for example. So the market was open and proven, but Apple provided real innovation in both technology and in digital distribution that wasn't there at all before the iPod. Combined, those were game changers and set Apple ascendant to the point it is today.
Getting most of the major record companies to sign on the dotted line is something I think only Apple could have done.