The advertising business has traditionally operated according to one very simple principle: marketers pay to pitch their products to someone else's audience. But brands are starting to think it might be time to develop their own audiences rather than rent, according to several agency executives at the Beet.TV online video roundtable in New York last month.Agencies and publishers are increasingly hearing this directive from clients in the last year, said two Beet.TV roundtable participants: Robert Davis, leader of the interactive video practice at Ogilvy, and Brian Quinn, VP and GM for digital ad sales at the Wall Street Journal. Less