As a kid I grew up in the St. Louis area, both on the Illinois and the Missouri sides. We called it Soda over there, no matter what state you were in.
I moved to the other side of the state to Kansas City, Missouri area to go to college, and learned that on the western side of Missouri it was no longer Soda and people gave you suspicious looks when you called it such. Over here on the left side of the state, it was called Pop.
Its sort of like the state name itself... on one side of the state it is Missoureeeeeee and on the other it is Missourah. Whether it is the fizzy drink or the name of the state, only politicians call it both ways or use the horrible phrase, sodie pop. At least in Illinois they all agree how to pronounce their state name and every single citizen is sure that there is no noise in their state name... the S is silent.