[giantrobot]

The iPod's initial release did correct some misfeatures of competitors but it was not a mass market success. It took Apple until the third generation iPod to hit mass market success. The first two generations of iPod only had FireWire connectivity, available on every Mac but very few PCs. With the third generation iPod USB 2.0 capability was added giving it compatibility with a huge portion of PCs.

Sales skyrocketed after the addition of USB support. After the addition of USB when the iPod took off it didn't outright kill the competition. It just sold so well and expanded the market so much that the PMP market became the iPod market and also-rans.

The iPod had a lot of competitors but no real competition in terms of sales. The PMP that killed the iPod mini (that was selling like gangbusters) was the iPod nano. I'd argue that the iPod was the opposite of a zero sum product because it expanded the PMP market far beyond its size at the iPod's inception.