You are right that at the end of day it is just a store. I know many people who keep renewing Costco membership every year but goes like once or twice a year. I on the other end is in same category that author describes. Even for gallon of milk I'd prefer going Costco and if there is more than one item it is not even a question.

To me most basic thing would be great quality at that price level that I guess everyone else is also looking for. At deeper level by reducing choice it sets a familiar pattern of food I eat on daily/weekly/monthly basis. Or for clothes just like people wear brands and proud to announce it. For me it is I do not wear brands and similarly proud of the fact.