Magazines Fuss Over First Lady, but Newsstand Sales Are Mixed NEW YORK -- Vogue's March cover story on Michelle Obama called her "The First Lady the World's Been Waiting For." No doubt she's been embraced by the media world, appearing on cover after cover, from Us Weekly to Newsweek. But when it comes to sales, Ms. Obama may not yet be general-interest magazines' new Princess Diana, who regularly helped the industry sell more copies at newsstands. A Michelle Obama cover doesn't hurt a general-interest magazine, the numbers suggest, but it doesn't produce more than an occasional lift either. New York...