A few months after I left Korea, my friends told me an inter-city bus was in an accident and actually tipped on its side. (Anyone still in Korea have a link to this story?)
I'm not sure if anyone was seriously injured, but perhaps some accessible emergency window hammers might have made a difference. But I don't know if this was one such bus in which the change was made...
I'm also told there was at least one English-teaching ex-pat on board and because he was not wearing his seat belt (as no one actually does on these buses - another issue, they often don't even exist), the Korean government and insurance companies are not covering any medical expenses...