It truly is a regional thing; like dory_the_fishie, I, too, live outside Atlanta, and have done so for me whole life, and here, politeness is a big deal. This rule is repeated through the Carolinas - where I attend camp every June - and Tennessee and Kentucky - through which I take a trip once a year. At my school, all teachers, administrators, staff, everything, are generally called 'sir' or 'ma'am.' Students, as addressed by teachers, are always Mr. and Miss.
However, in Chicago, where the majority of my family is from, and where my parents are from, I rarely hear formal addresses like here in the South - the reason I never used them much. Because of my parent's background, as a young child I was not raised to use sir and ma'am and similar addresses, but once I entered school, I began to out of the understanding that it was a sign of respect. However, the majority of my friends, who were almost all raised in the South, are always extremely polite to everybody. Basically, even if it's a stranger, here, you treat everybody with the respect you would use when talking to a teacher or trusted adult.
In New York City and other areas along the Eastern Seaboard, another area I go to often, most of the people you would associate with as a tourist, like shopkeepers, taxi drivers, etc., are also polite. They may not call you sir or ma'am, but they will treat you nicely, smile, and generally do whatever it takes to make you comfortable.
In California, I see less of this, and no, I'm not stereotyping. Most Americans won't talk down to strangers, or anyone they don't know extremely well and associate with often, but in California, there's a lot less, well, Southern hospitality, I guess, than there is in the South. Obviously. The people are fine, and they don't talk down to you or anything, but they're not going out of their way to show respect. (No offense to California - this is just my personal experience, I'm sure that there are many wonderful people there!)

Generally speaking, most Americans are fairly polite to strangers, as well as authority figures. This is rarely carried through to people like parents, friends, etc. It does very a lot by region, though. In the South, you treat everyone as if they're the person you hold in the highest respect in the world. Some areas, like, in my experience, the Midwest, everyone's your best friend, and in some areas, everyone is a customer. There's a lot of freedom, but yes, as a general rule, we're all pretty polite. The difference is really how it's manifested.