This thread basically confirms my personal experience of different places I've lived or travelled, which is that the northeast is more like the south in this respect (though less extreme) while the upper midwest is more like Canada (though perhaps again less extreme).
In Ontario I would never call anyone, be called by anyone, or ever hear "sir". One summer in university I had a low-level customer-service position in downtown Toronto and it quickly became obvious that calling me "sir" was a reliable American-tourist shibboleth.
I don't know the south well, but even a brief trip to Georgia is enough to make it clear that many people use "sir" or "ma'am" even after the conversation has started.
New Jersey and the NYC area generally aren't quite like that, but the term is still common in public business. A waiter in a restaurant will ask you "how can I help you, sir?", and a transit employee or security guard would say "excuse me, sir" to try to get your attention or answer a question "yes, sir". I found this quite surprising at first, but I got used to it. It is probably in decline among younger people though.
In Wisconsin it's perhaps not completely unheard-of due to the greater influence of the rest of the US, but it would still be rare for anyone in a store or restaurant, in either direction, to call anyone "sir" or "ma'am". I don't hear it in the ordinary course of daily life.
Yeah, it's probably a cultural thing. If it is used at all, it's either sarcastic or ironic.
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