How many people visited Style.com, the online home of Vogue and W magazines, last month? Was it 421,000, or, more optimistically, 497,000? Or was the real number more than three times higher, perhaps 1.8 million? The answer — which may be any, or none, of the above — is a critical one for Condé Nast, which owns the site, and for companies like Ralph Lauren, which pay to advertise there. Condé Nast...