I've always felt that "know thy audience" becomes a form of stereotyping. Certainly, in this or that design you'll get to know, and meanwhile learn to incorporate, facts and measurements of a special group of people. An ATM should really work for everyone who might have a bank account. But there's a big difference between "usability" and "targeting an audience." Usability doesn't pander, it just makes accessible and comfortable. Audiences, though, are too often pandered to.
