The post office along with anything the government (military, FEMA, etc.) ships doesn't even remotely close to a competitive rate. God bless pork!

Amazon is seeking to become a fulfillment company be that in server farms (their big money maker now) or in fulfilling orders to customers. Amazon wants to store somebody else's stuff and collect fees all up and down the supply chain without having to put a lot of their own money into the mix unless that money comes with profit.

Amazon is changing the status quo the same way FedEx did 40yrs ago. Just as everyone thought Fred Smith was crazy, everyone thinks Bezos is crazy. Time will tell but it is a pretty smart way for them to shrink costs by slicing out middlemen.