What Amazon are doing is nothing new, what is relatively new is the resurgence of customer service. Amazon Logistics works with local and regional delivery service partners across the country to deliver Amazon packages to customers seven days a week. The Amazon Logistics service compliments their current large, national delivery partners and provides additional capacity as more and more customers use Amazon Prime's next day delivery benefits.
Note the word partners, these are companies that agree to sell their goods and services through the Amazon name, Amazon do not allow for any shoddy service, believe me, they crack the whip.
The system used, to get an order from supplier to customer, is known as hub & spoke (look it up) it's a system used by others and it works very well. I just wouldn't want to be the delivery driver turning in at six am to find that I have about a hundred deliveries to get through. Many of those drivers are self employed, and do they earn their money.