A carseat is not going to help in a head-on with a logging truck OR a nose-dive into a major metropolitan area. It WILL help in a fender-bender, a crash landing, a water landing, or during turbulence.
Obviously it's not going to save you from a fireball but it wouldn't in a car, either.
This is just not true. What about the water landing in the Hudson when there were sudden drops and jolts and it would have been really hard to hold on to a baby, BUT in which everyone got out alive? Honestly, most plane troubles do not lead to flaming dives. That is one reason it is safer than driving.