Yeah what jimrtex described is a "float" here.
Do people in the south seriously refer to Sprite, Sierra Mist and 7 Up as "Coke"?
Not exactly. Where I live, most people ask for the specific beverage if they know what they want. For example, if we want a Sprite, we're not gonna say "Gimme a pop", "Gimme a soda", or "Gimme a coke", we'll say "Gimme a sprite". If you're at a restaurant and ask for a coke, you'll get Coca-Cola. If you're in my house and ask for a coke, you'll get the same. However, I've heard people ask them to "get me a coke" if they are at someone else's house, to which the other person asks, "What kind? We got ..." but if you're out in public, you'd ask "What kind of drinks do you have?", with no reference to pop, soda, or coke. But that's just Georgia. Coca-Cola is the dominant beverage in the South and when people ask for it, it's normally what they want -- not a generalized term for beverage.
Fine, you guys don't use Coke for everything soda related.
But then why do you guys answer the question with "Coke" then?
Poll : Do you call it soda or pop?
Everybody in the South : We call it Coke!
The rest of the country : wait, what? You call Sprite or Dr.Pepper "Coke"?
South : no that would be stupid.
The rest of us : ba wha?