See an actual Coke should be called a Coke, but these idiot southerners call Coke and Sprite and root beer and anything else brown or amber colored "coke."
Oh and they call everything clear Sprite, so a Sierra Mist or 7Up is simply "Sprite."
I'm not Southern myself but sure as heck a crudload of people I know (including all my relatives) call it Coke. Reason why? It's the most popular brand. It's the same as why the rest of my family call all detergents 'Tide'.
You can argue that Coke isn't the most popular brand, but to us and my culture, it sure is.