All types of addresses, pedantic clowns -- specifically rural addresses. If UPS and FedEx didn't price discriminate against rural customers (and had a broad universal service), there would be no need for the 1st class delivery monopoly.
The employees are still available to work; Some spend a few hours on standby and then move back to the floor when a shipment of mail arrives.They are still available to work. They are put into standby until a delivery is made. If someone (who would have been on the floor sorting mail or whatever) calls in sick then a mail sorter person who would have had been on standby had the other worker not called in sick would be put to work filling in.
There are very few zip codes outside of alaska where there is a rural fee, and it's there for a valid reason. Usps wont deliver to their doors at all, but you cry because we charge more?
I already stomped on your theory though.If you're going to argue that having trained workers on standby is beneficial, then you're going to have to address the problem of laying off non-career employees whose purpose for being hired is to inexpensively pick up the slack.