I heard that the reason that you can only use 150g discs in Japan is a consequence of someone getting struck in the head and killed. This is water-cooler level gossip though, I don't know it as a fact. Come to think of it...I've only heard tell of the "150g in Japan" rule, so that part is hearsay too.
Anyone confirm/deny this?
I think the first part is just urban legend, but disc weights are restricted in Japan. It used to be nothing over 150g was allowed, but at the most recent Japan Open pros were allowed to throw up to I think 159.4g, not sure if that's going to be a change for everyone or not.