Coke is constantly beaten by Pepsi in blind taste tests. Coke controls it market share through advertising. It presents itself as a hipper product and people in turn want it, even if they actually prefer the taste of Pepsi.
I've been hooked into the Pepsi challenge three times and Coke kicked ass every time. My sister-in-law likes Pepsi so we keep it on hand. I go through 20 towers of Coke for every one of Pepsi.
This "Pepsi wins" urban-myth is the logical result of advertising. People believe it even though it isn't true.