I read on Pricescope that in Japan Mikimoto calls their top grade pearls "Best of the Best", while in the USA the company uses "AAA" for their top grade earrings and "Reserve" for their top grade strands.
The brand means something to some people. I think that is clearly the case. And no judgment; we all have our own family histories and reasons why we prefer any given thing over any other given thing. But it doesn't matter to me-- not for pearls, anyway.