Right, but this is the same company, so the cost of marketing, auditing, R&D, etc. shouldn't be different for these products. That's a fixed cost for the company.

This is a guess, but the argument is probably that it took way more R&D effort for them to figure out how to produce it efficiently in the US, and they've chosen to increase the cost of the US phone variant to offset this particular R&D expenditure that the Chinese variant didn't have.