The problem with the Post Office, is the cost of upper management. Most PO workers make great money as it stands... but the MGT? Make unreasonable salaries:
http://www.savethepostoffice.com/it-was-very-good-year-salaries-usps-executives As for Fedex... firstly, its not related to any part of the Govt. Its as Federal as the Federal Reserve.
Next.. Fedex is comprised of many private 'Route Owners'. You can purchase a route, then you buy / rent trucks...
and take employees from the base office hires. As a Route owner, you dont actually have to run a route yourself. Some do. I believe the route owner decides the rate of pay, as well as the hours you work. A Percentage of the money made from each package, is sent to the route owner. A sort of commission system. With that money, you need to pay the employees, as well as truck payments, fuel, and repairs.
The routes make Mega $. However, the workers themselves... not so much. And these guys work very long hours, and are running and lifting heavy stuff all day and night long. Im not even sure that many of the guys have health care.
I believe this private ran stuff keeps a lot of the expenses away from the corporation, which allows them to keep the prices of shipments much lower. It probably screws over the general workers however... depending on the Route owner.
I think UPS is ran completely corporate, rather than with individuals purchased routes. As such, its probably more expensive than Fedex. I dont trust UPS, due to their losing a 37" lcd tv. How do you misplace a box that big?!
USPS, is a govt. agency.. and like anything Govt.. theres huge payouts to upper MGT, corruption like you wouldnt believe, lax attitudes about getting things out, schemes to cover things up, and more.