I work in Shipping for my company. We do not use USPS because we can not track the package. We've had to many customers say that they never received the package using USPS. When they loose the package and the customer service from USPS SUCKS!!! what good it flat rate postage. My company has negotiated rates with UPS and FedEx even with that we can't ship anything for less than $11.00. And then if it is a residential address and out of the 'normal' zone (whatever that means) then there are extra charges. And if you are shipping outside the continetal US the charges are way higher.
I, on behalf of my company, have spent hours...days...trying to find ways to reduce shipping costs. Most companies loose money when it comes to shipping.
Just FYI from someone on both ends of the Shipping debate.