Smile for smileys!

Why do not people smile? I am in touch with people from all around the world. Germans, Chinese, Canadians, Americans all of them with very few exceptions greet each other with a dead pan face. They are definitely not morose or depressed people who are feeling down and out. They do have their laughs and jokes. Its just the greeting that I am talking about. Saying 'Hi, how is it going?' with a smile is definitely cheerier than with a poker face isn't it? Sometimes I wonder if my smile is kind of a leery one or something, one which condescends and makes the recipient wary about their response. Or is it because they think that smiling makes them lose something? Like this one incident I had in a cafe. I was standing at the counter waiting for my order when I looked back at the queue and saw someone I knew. This guy is hefty, huge, looked like he hadn't slept well in a week and was looking at me pointedly. So in response to the recognition, and being a bit conscious of all the people looking ahead, I gave him a nod (instead of the shout of joy and crazy arm waving with a dazzling smile he needed as he let me know later on). He is again one of those guys who doesn't smile much. Laughs a lot, usually making fun of other people/pulling someone's leg but not the smile because you feel like it kind of guy. What I was getting at was the 'tough men don't smile - they just nod or ignore' syndrome. The thing I am talking about is meeting someone you know on the street or in the corridor, and the casual smile. Nope, that is very rare around here. Of course then there is the other side. The one wherein you keep running into the guy you said hi and exchanged smiles with a couple of minutes back. Or the situation where you see someone who is going away for long and exchange pleasantries and say tearful goodbyes to only to run into him again and again a few minutes apart. Then there is the embarrassed, strained smile. Well I have piddled enough, all I want to say is, smile people! It doesn't hurt and it lightens the air!