Interesting post, yes, correct I also find that most Turks have a very serious non smiling face, once you get to know them you learn that they can laugh and smile a lot. It is the opposite of North Americans. But remember when Turks smile it is real which you cannot say from North Americans. ( mostly then).
That´s generalization. A smile is a smile here (in North America), we may smile at strangers to acknowledge them, and most people who smile are genuinely nice or kind. If they didn´t, there´s reasons , such as in Turkey, it can be mistaken for flirting
, maybe someone got chased by a man or woman
, maybe there was death in family, break-up, etc.... There´s always reasons, please don´t generalize.
and about not smiling at people they don´t know, they are awesome lol 
They don´t deal with strangers. That´s a pretty good thing. Once you know them, you´ll know who they really are!