You have a point with the old and disrepair but fatal accidents is a bad classifier because what proof do you have that fatal accidents of other cars are fatal accidents of a model S and by fatal I am assuming you mean fatal not due the fire.
As for running over debris, again it is not important because who cares if gasoline cars have different causes for their fires vs the causes of the model S. What matters is the percentage that actually do catch on fire with a large enough population.
After that, the next question that should be asked is, what is the difference between the danger of these fires. Are gasoline fires more or less dangerous.