I did a simpler but similar analysis when the iPod first came out. I considered these three factors:
- Size / weight
- Storage capacity
At the time of the original iPod, you could get devices that beat it on one or even two of those points, but you could not get one that beat it on all three. The iPod was (I believe) the first device to make use of 1.5" hard drives. Until then your only choices were flash storage, which was small but at the time had very little capacity, or 2.5" hard drives such as the Archos players used, which had lots of storage but were big, heavy, and ate battery. The 1.5" drive from Toshiba was a way to hit a size / weight / storage capacity niche that had never been achieved before.
And that's not even taking into account the factors mentioned such as the fast data transfers via Firewire or the click-wheel UI (which was a breakthrough in usability at the time even though the original iPod was mechanical unlike the later touch-sensitive models).