The store I work for (a local office supply store) also does UPS shipping for the public. We do charge a flat rate fee over the actual cost of shipping that covers our time spent and the fees that we pay UPS for them to stop by and pick up from us every day. However the fee for insurance is very reasonable, and claims are usually taken care of quickly, although you do often have to argue with them a bit about how well the package was packed...the standard response is insufficient packing material! We ship out several packages a day and usually have 2-3 claims per year. And sometimes it WAS insufficient packing material put in by the customer.
The only way a regular size package would be $72 to ship would be if it was sent Next Day Air and was heavy to boot.
I'm guessing that the $40 from the post office would be very comparable to what our charges would be.