In addition to the Japanese (constant) and Australian (recent) shoppers, a good number of mainland shoppers will also desire purchasing designer/luxury items in Hawaii due to the lower sales tax (4.5% Honolulu, 4.0% elsewhere I believe).

For instance, a vacationing Californian who really wants a certain pair of Prada shoes or LV purse, would pay less in Waikiki (4.5%) rather than in Beverly Hills, Newport Beach or San Francisco (7.25% to 8.75% - ave 8.25%). Maybe not much, but you know how some shoppers will try to rationalize purchases

And I've never noticed any discernible difference in luxury good pricing between designer stores in Waikiki/Ala Moana vs Beverly Hills/San Fran. It's the exact same price for the exact same item.