The trouble with the theory is that the seats on the buses I rode on were neither particularly high nor particularly soft. On the bus I rode regularly, the back of the seat in front did not have exposed metal, but many in my town did. Frankly, the fabric covered ones were not much better as you could feel the metal bar beneath the fabric. Even as a kid, I knew I was likely to get seriously injured in the event of an accident. Thankfully, accidents are rare. Perhaps, newer buses are somewhat better, but I imagine most of the old ones are still in service.