I think bjornhall is on the right track. I've had a close look at at least 8 serious crashes of light aircraft. Not one of them has had the 'great big lump of engine' infringe on the passenger cabin by very much.
In not one of these incidents was the airframe so distorted that the pilot and passengers could not escape. Two of these incidents were at very high speed and were simply not survivable, deccelerating from 150 kts oddd in the space of a couple of feet does horrible things - but the airframe whilst pretty bent did not compress much and we could easily access the interior.
I would certainly agree that some airfrqames are more likely to have crashes. Either due to the type of flying the airframe does - or foibles in their handling.
Modern airframes do protect the occupants rather better but the nut behind the wheel is a much bigger influence on accident rates and accident types.