Earlier quoted context omitted.
The point is that transaction is not profitable but overall the system is. They get soaked on the 3c button, but as most people dont do this, they can absorb that cost and subsidize it with the rest of their profits.
Fine, but why would they? They're running the system anyway, sure... but why take a marginal loss on that 3 cent transaction?
Do you pay more for web pages from China than you do from the USA because they travel further? Why not?
The problem is that the whole accounting and tracking overhead would be far more than it's worth.
The only real issue is whether the total income from carrying traffic is bigger than the total cost of running the network.
Yes, there are anomalies with China because Chinese charges reflect Chinese costs (and government subsidies, if any). The fact that USPS has higher costs is not something the Chinese have to worry about -- or not until the US negotiates higher fees via the Universal Postal Union.
Otherwise, the USPS charges a lot for overseas mail, so it makes extra profits when that mail is delivered in low-cost countries such as China and India. On the whole, it probably breaks even or comes out ahead....