It depends. A high-volume, low-margin retailer would save a huge amount from 20% on transactions. If Amazon were motivated to take on the risk of building the

It depends. A high-volume, low-margin retailer would save a huge amount from 20% on transactions. If Amazon were motivated to take on the risk of building the infrastructure, this could happen quickly. But, they have other things to focus on, and I doubt they would make the calculations in the same aggressively optimistic manner.