"Oh Shit" moments...

No I get that. But manslaughter's fairly straight forward isn't it. No one is saying that the guy intended to kill the admittedly negligent motorist, but the result of his road rage based attack was that the guy lost his life. It's a shit situation all round but if I punch someone and they die, it's my bad.

Indeed. It's an established principle in law that one takes one's victim as one finds them. If they happen to be vulnerable in a way you or to a degree you don't expect, tough (on them and you). http://en.wikipedia.org/wiki/Eggshell_skull