Oh yes that's DEFINITELY a northern thing. Even southerners are confused by that. Londoners especially seem to think you only say hi to people if you know them.

A friend's father told me about the culture shock he felt when he first went to a bigger city and learnt that strangers don't greet eachother there. Similarly my friend being mistaken for the second coming of christ during our early teen years trip to London was a fever trip we won't forget.