Does speed really matter, though? I mean, the issue with cars is that they sometimes come to a very sudden stop, and in those situations the passengers need to be bolted to the ground. Planes don't often come to very sudden stops and when they do, bolts don't matter much.
The seats need to be secured, yes, but not in nearly the same fashion.
Yes. I would say even more so than cars. Even at its slowest a plane is traveling at 3x the speed of a car or 9x the kinetic energy. Then you have the problem of a compounding failure. If even one passenger gets lose the seat in front has to do 2x the work. A plane with 30-70 rows can have a domino effect if the bolts don't hold.
Also cars don't instantly stop. Most of the energy is dissipated by shedding the engine under the body and crumple zones. They have a dramatically shorter runway than planes.
The seats need to be secured, yes, but not in nearly the same fashion.