Its hard for me, maybe too much of the 'tism to be able to not take people literally. All of the people i have actually talked to about it don't actually feel like it is "just a custom", they aren't operating at that level of abstraction. They think they mean it, or at least lie about it afterwards. It seems fundamental dismissive to their intent to blatantly lie.
I suspect i would have similar issues in other places as you describe them.
I'm from Midwest America and do this. I think what makes it weird is that it straddles the border between sincere and insincere. What I really mean is something like, "Hello fellow human, fare thee well!" <Tip of my hat> I actually do wish well for you as a fellow human being, but I also know that we aren't acquainted and so it would be inappropriate to be overly familiar. It's meant to strike that balance, but it's often taken to be all the way to one side of the spectrum or the other (fake or expecting an intimate, detailed response).
I suspect i would have similar issues in other places as you describe them.