By Daniel Kline Both fast-food chains have tried to offer something very different (and Burger King’s new menu item certainly counts as that). Fast-food chains have a long history of trying to serve as broad an audience as possible. That has led to endless experiments designed to expand their audience beyond the people who crave unhealthy food or those who value convenience over their health. A McDonald’s (MCD) – Get McDonald’s Corporation Report Big Mac or a Burger King Whopper has never been marketed as good for you. When you drop in on Ronald McDonald and friends for a meal you understand t…