"The Post Office is privatised in the Netherlands and works just fine. Japan is about to privatise their post office. Britain has opened its postal service to competition and no ill effects."
How huge is the delivery area for the Netherlands? How about Japan? Most private forms will not deliver to out-of-way areas. That's what keeps them profitable. They can chose where they'll deliver. If it's not profitable, tough.
The USPS has to delivery everywhere, including isolated areas in Alska, for instance.
I will double check, but I believe the Post in Australia is privatised too; thus the argument about out of the way areas is moot.
That said, there are plenty of out the way areas in Britain too. Yet the Post Office is commercially successful.
Regards, Ivan
Higher rates to out-of-the-way places would result in costs to deliver to more populous areas dropping. End result: everyone gets what they pay for.