Paul. The servos are not just used in Jets, they get burried in wings on 3-D aeroplanes, 3-D choppers and they waggle a lot, in very hot countries.
I've run tests on a bench with constant movement (no load) and can get a metal cased servo to 45+ degrees easily. The gears don't generate the heat. You are right that in a jet we make small movements and fly fast, but again I have installations where the servos are mounted say above a tail pipe in the fin and on a hot day you would be surprised how hot they are running.
You are right about the pins and wear, its a big thing in petrol models, I change cases more than gear sets.

Dave

Its the old game of many scenarios