Lets go to Merriam- Websters Collegiate Dictionary shall we,
www.m-w.com
Main Entry: soda pop
Function: noun
Date: 1863
: a beverage consisting of soda water, flavoring, and a sweet syrup
So the midwesterners are kinda correct when they call it POP, I dont call it pop nor will I ever call it pop, but websters does
Main Entry: Coke
Pronunciation: 'kOk
Function: trademark
-- used for a cola drink
So Coke is used for a cola drink, so that means pepsi can be called coke as well according to websters. But not fruit sodas.