Why only diesel spills?

Don't ask me how it's done, but i was always led to believe that some truckers / van drivers do it deliberatly so they can get an extra few miles done before the next fuel stop...

My mate, who is a trucker, was recently recanting a story about a run in he had with a fellow trucker he seen doing just this. The response was along the lines of "sorry mate, I didn't realise it could kill someone". That said, I was drunk at the time and may have picked him up wrong...

Anyone else out there heard of this?

I suspect a lot of it is caused by people losing the original caps, and using cheap and ineffective replacements.