This will continue to happen, at least with the Model S. The Prius' battery pack is tiny in comparison, and far better protected. Gas tanks can of course catch fire and explode, but they too are much smaller and better protected. The Model S battery pack contains over 7000 lithium-ion cells, any one of which can catch fire if damaged as in this case. The Model S batteries are located underneath the floor of the car, occupying almost the entire exposed underside. This location is desirable for the car's low center of gravity and potentially for replacing the battery pack, but is also the most likely to suffer damage from road debris.