I know the post office has a lot of problems. I have known a couple of long-time post office workers and the horror stories they tell will make your eyes bleed. But in their defense I can't recall sending a letter, or expecting one, that didn't get to it's destination as promised.
No doubt that “Universal Service” is a big issue to the USPS. Part of the problem is that there is no distinction in charges for rural delivery. Both UPS and FedEx charge differently for delivery in those area’s. the other part of the problem is the rationalization and optimization of their networks. The USPS has not gone through that process nearly to the extent as UPS and FedEx have. There is very little incentive for the USPS to do so as they are not held accountable by shareholders like the two private carriers are.