In Japan, you don't just walk up to people and strike 
    up a conversation. Foreigners might, but native Japanese 
    largely don't.
    To establish some sort of repertoire, you need to share some 
    sort of acceptable social context with that person: went to 
    school together, played on a sports team together, work
    together, etc.

Are there really places in the world where total strangers strike up conversations and form friendships with people on the street, on the bus, etc?

I'm 41 and I don't think I've never experienced that and I'm a pretty social guy!

Aside from random "how about this weather?" chit-chat, I don't think I've ever befriended somebody outside of an existing social context like school, clubs, workplaces, online communities, fellow pet owners, neighbors, etc. Closest counter-example I can think of is my mom, who become good friends with a cashier at the supermarket she shopped at twice a week.