There are knock off's of everything now... very few wheels that come out are of "new" design. Lenso for example specialise in replicating popular wheels designs for a much lower cost.
Why pay for originals when the copies are just as good, and cheaper to buy? So to answer you question, yes, more than likely there are knock off's... by your own addmission the US versions are only "slightly different / better". Is it really worth the extra cash for a slightly better looking rim?