Here in Tennessee, it is not only considered polite, but it's really kind of expected to say "ma'am" and "sir."
In fact, my kids are considered to be behaving disrespectfully at school if they don't refer to their teachers that way.
Also, I'm not originally from here, so I did not raise my oldest son to say 'ma'am' and 'sir.' This caused a lot of issues when he was younger, and he's learned to adapt. My younger son still has a hard time with it, b/c I don't enforce it at home. Yet at school and pretty much anywhere else, it is expected.
Another thing: if a parent asks a child a question, the child responds with, "ma'am?" instead of "WHAT?!" I think that's kinda weird, but it's just the way it is down here. All of my friends' kids do this.
Even at work, when I'm on the phone with someone, or someone asks me a question, I respond with, "yes, ma'am," or "no, ma'am." I wasn't raised to do this, but I've adapted to the TN culture.