The high-energy infrastructure is the car trip to "local", not making additional use at the margin of mail trucks which would travel the same streets regardless of whether they had another case of organic blueberry jam on them or not.
If using UPS/Fedex, you get the fuel surcharges, residential charges, and rural charges that can make a small profitable order become unprofitable (and cuts into profit margins of others). It can even be almost $10 to ship a 1-lb package in-state if to a rural area. And then you have to consider box cost, and void fill cost. I switched to USPS last year for 90% of my shipping, and it's still a loss at times from what I charge for shipping.
No, but almost everyone can take advantage of Amazon's discounted rates.
http://www.amazonservices.com/content/fulfillment-by-amazon....
It won't work for shipping food, but it can be a real money saver for non-perishable items. You don't even have to pay shipping costs if you sell the items on Amazon.com, just pay the fulfillment fee and the customer can use Prime or Super Saving shipping.