Barriers to entry
The Zappos site is kind of ugly, while Piper Lime is pretty. I have no doubt that Gap thought the better personality, design etc. of their service will trounce Zappos.
They both have free standard shipping, both ways, they both have good product image shots (a Zappo speciality for many years). But the Gap is pretty and Zappos is ugly.
Online companies seem to think that prettyness=a good experience. I'll bet that Zappos customer ratings (focused on fit) and wide selection will do a better job of selling shoes that the pretty Piper Lime.
On the subject of barriers to entry, franchise wine stores are popping up all over (Best Cellars, Vino 100, Wine Styles). I had such a good experience with Best Cellars in Boston (after being initially skeeved out) that I'm looking forward to trying Vino100 in Los Altos (although I'm currently skeeved out). There seems to be nothing that distinguishes these stores from each other.