You're missing the point. Shipping from LA to NYC in X days should be cheaper than shipping from Shanghai to LA in Y days PLUS shipping from LA to NYC in X days. China Post charges some amount to get from Shanghai to LA, and they do that slowly. At that point it enters the USPS system, and they deliver the package to its final destination in NYC. But by UPU rules, the USPS has to charge less for that China Post package than they do for a package that originated in LA, even though they use the same infrastructure.