Amazon and the Last Mile

In Retailwire:  Amazon plans to own the last mile.  " .... Authenticating rumors in the marketplace, Amazon is indeed testing its own delivery network in the U.S., according to an extensive report last week in The Wall Street Journal. ....   How important is it for Amazon to eventually establish its own wide scale delivery network? Is the over-reliance on major carriers a weakness in the e-commerce model for big online retailers?  .... "