Maybe my point wasn't clear - what I am getting at is how comes Poles say hello to each other specifically (and bizarrely to me) at the doctors, but apparently nowhere else.
No, it was clear, and I hope you didn't think of my reply as a rude one, I just wanted to say that every nation (or local population) has tradition and customs that differ and you can't be desparate about understanding it all at once. It will come with time, or you simply need to be a little more open-minded than normally to see there's nothing strange. Just because something is not the way you are used to. For example (from a thread about strangest things in Poland) - some people saying a washing machine in the bathroom (which is a better, more suitable place for it
) is strange, for me (and my logic) a washing machine in the kitchen
is actually much more unusual, but strange? Hell, no. I'd start thinking it's bizarre if it was placed in the living room :)
And I don't have the answers you need, but for example greeting the other patiants in a doctor's waiting room, could be drawn from the fact that they are your fellow brothers in misery (you are or are afraid of being ill, it's always some kind of misery), so you feel more empathic towards them, hence you become closer. This is just a try, I'm not even sure if it's the real reason.
While greeting complete strangers in the streets of a big city is rather completely useless, because you probably never talk with them (or even meet them again).