True. At the end of the day, Zappos is/was really just an online shop. Amazon at least were the first/biggest online shop in a field where infinite shelf space means a lot. Shoe stores on the other hand, could easily have been bigger if bigger meant better. What strong reason was there at the time to believe that Zappos would grow so much more then the many other online retailers with similar numbers.

Growth: http://i.zdnet.com/blogs/zappos-revenue.png

YC's 'How to Apply' recommends against saying you will win because your app will be well-designed and easy to use because presumably that is what everyone tries to achieve. Zappos eventually succeeded because they made the online shop equivalent: efficient back-end, excellent customer service, lots of products that people want to buy, low prices.