I am surprised that someone who is a foreign national with a single entry visa to the USA would not have a problem because when you leave the USA for international waters (for duty free, gambling, etc) logic would suggest that upon your return you are entering the USA again, even if you have not entered a second country in the meantime.

The same issue should arise if someone with a single entry visa for the USA does a milage run to some country where they stay airside in a transit zone. In this case, they do go through customs and immigration upon the return to the USA and I don't know how CBP would be able to tell whether they ever entered the country at the destination if their passport hasn't obviously been stamped or a visa for the new country used.