Why the iPod won the PMP market
The reason why the iPod became such a phenomenal hit was it succeeded across all dimensions.
Hardware - Cool, stylish. Best fit & finish of all PMPs. Best combination of HDD & battery life.
Software - iTunes for buying music and syncing to the iPod. Better stability and quality compared to other sync software and better selection then Napster for buying.
Advertising - getting the likes of U2 to shill for it. Having cool looking billboards everywhere.
No other company could combine all these aspects, thus Apple was destined to dominate the PMP market.