I don't think that's entirely true. Look at the past events. When there have been multiple clubs from the same country (USA) in the defender series, if a boat from a club other than the host club won the defender series, my understanding is that she would sail in the finals on behalf of the host club.
Not sure that it ever turned out this way, but that has been the main concern about if the cup could ever return to Newport. Common knowledge is that it would have to leave the country, and be won back by NYYC (or another club in the area).
Maybe that has more to do with the specific "agreed protocol" for each cup, which is what the monohull fans use to drive their goal of match racing with similar boats. (And for those of you who want to reiterate your idea of what the DoG says, it's almost irrelevant when an agreed protocol is used.)
