I'm Canadian and I only really get "Ma'am" when I travel in the States. It makes me feel a million years old. But I also know it's people being polite and actually I do really appreciate the general American politeness and friendliness and attention to customer service, etc. I live in the UK and as much as I love it, people in any type of customer serving positions tend to be pretty rude here by North American standards.
Anyway, I don't have much to add here, I think you/the other people who have commented are on the right track. It's interesting because I have an American friend (who I met here in the UK) who has spent a lot of time in the Middle East. She'd probably have something to add. She has studied Arabic extensively in Middle Eastern countries, spent time living and travelling there etc. I know she has told me that if Arab people have a teacher who they really respect they are likely to call them something like "Professor" even if the person isn't technically a professor. But those are actual Arab people we're talking about, not foreigners or whatever.