I think it comes down to the type of driving the two vehicle types do:
Most Coxsters spend most of their time safely cocooned away in a garage, and only driven on weekends in perfect conditions by enthusiast drivers who place great pride in their driving ability, and take great pains not to get involved in accidents. Most are also not winter driven, therefore usually won't be out in snowy or icy conditions where accidents/collisions abound.
A Prius, on the other hand, is a commuter car, driven by people of all kinds of driving skill (or lack thereof). They get driven at all hours of the day, in every condition imaginable. Worse yet, they are primarily used by taxi drivers, therefore a typical Prius could very well see 100 000kms/year, greatly increasing the likelihood of being involved in a collision or accident.