Maybe I should change the question slightly to try and gage your opinions - to to make clear what I'm trying to understand.
If there were as many light ga aeroplanes in the air as cars on the road (air-space permitted) would the rate of engine failures in cars and aeroplanes have been similar? (Throw in a nice mix of types of light aircraft as you would have different types of cars on the road too).
If not .. why not?
PS - Not that I'm bored at work asking questions like these btw.