The show was based in part on writer Candace Bushnell's (a female) book of the same name, compiled from her column with the New York Observer. Bushnell has stated in several interviews that the Carrie Bradshaw in her columns is her alter ego; when she wrote the "Sex and the City" essays. Though the gay theory works, most of the executive producers, producers and head writer were women.
And, at least in the big major cities (NYC, SF, LA, Chicago, Washington) there is no shortage of highly educated professional women who are basically using conspicuous consumption (itself an idea from the 1899 book, The Theory of the Leisure Class by Thorsten Veblen) to conceal? substitute? ignore? the basic truth, which is, in the end, they are shallow, superficial, and self-absorbed. Which is why I find it realistic.