I have asked this question many people and surprisingly haven't really gotten a straight answer from anybody:
If an American company manufactures a product in China and then sells it in the U.S. don't they have to pay an import duty as well (which everybody assumes applies if they sell it in the European Union)? Sure, import duties (for a particular product) might be different for a product manufactured in China depending on whether it imported into Europe or the U.S. But then the opposite question applies for a European company producing in China and selling to the U.S. and the EU: would it pay higher import duties for its products going to the U.S. than for those going to Europe just because its a European company?
American auto-makers have to pay import duties when they manufacture cars abroad (which is why NAFTA boosted the creation of new Mexican car plants manufacturing GM, Ford and Chrysler cars, as it reduced or even completely removed those duties).
My notion has always been that the argument that one reason why 'U.S. products' [that are actually manufactured in China] are more expensive in Europe is that there are import duties to pay for those products when they go to Europe but not when they go to the U.S. cannot really be true. Now trade agreements including free trade zones often include clauses that take the 'local content' in a product into account, meaning how much of the value of a product and its components was created in which country. What I don't know is whether (a) such clauses exist for products imported from China to the U.S. or Europe and (b) whether 'intellectual property content' (including the actual research and development costs) can influence custom duties.