It comes down to comfort I think, in some cases anyway.
I've met a lot of really seeminly rude middle eastern tourists, they always look like they're mad, or maybe like a frightened dog or something.. But a couple I've just, you know, said "hey" too and smiled and got great results, they were really happy to be able to talk to me. I guess there is a lot of prejudice towards them.
Japanese, pretty damn polite 'round here. Must be the American Japanese Billy keeps on talking about, but the ones from Japan are immaculately polite. The French, and the Germans both appear to always be angry, ESPECIALLY when they're talking aloud. Especially the Germans. "Good morning" sounds like "GTFO out of my kitchen b**ch!", then add alcohol and you've got people who don't know the deal thinking there is gunna be a fierce gun battle going on between the two German guys who appear to be threatening each other.
Actually speaking of which, my Grandpa (not exactly a big fan of Germans) works with a German guy in construction, or he used to anyway. So one day something is not quite as it is supposed to be, something minor. So in a joking way, he says to the German guy who is, for lack of better term, "at fault" and says "Vost ist los" (spelling obviously is probably wrong, but it means "what is this?" and the german guy responds all happy that someone spoke some German, in German, and frightened the guy that my grandpa was working with (who was a lot younger) and said afterwards something about what was going on, thought he was going to start a fight just cuz of they way they speak.
"George Bush says he speaks to god every day, and christians love him for it. If George Bush said he spoke to god through his hair dryer, they would think he was mad. I fail to see how the addition of a hair dryer makes it any more absurd."