The first iPod had the wheel, which was the revelation. The later clickwheel was just an iteration. And the iPod had FireWire, which meant you didn’t have to wait all day to move your music over USB.
Apple didn’t come out with USB support for the iPod until USB 2.0 became a common feature on PCs, with it’s theoretical speed of 480 Mb/s (in my experience of real-world use it was actually still slower than FireWire 400) and sufficient power.