Well Stormcat, his death wasn't exactly caused by motorcycles, but it was definitely motorcycle related.
For anyone who hasn't read what transpired, here's the Cole's notes version:
Fellow decides to go on epic tour from US to South America.
Hits a donkey in Mexico, breaks his back, and is a parapalegic, feels nothing from mid back down.
Eventually commits suicide.
My take on is that his being disabled really took it's toll on him, and he mentally couldn't living that way, and that's what drove him to suicide.
I'm reading his book now actually...