Americans, more a question about you!?

You are partially correct. In many areas like you have named, the majority that live in a particular city support the team that represents that city. However, this isn't 100% true. I am finding more and more fans who are fans of teams that do not reside in the same state or city they live in. In other words there seems to be an increase in numbers of fans that support a team regardless of where it is on the U.S. map. Of course the percentage of fans that support a team because of where they live or grew up is still higher, things are not always concrete in that sense because when you have choices, you usually end up making the choice based on preference and not always where you live or where you grew up.