"For example, when everyone's encouraged to bring hand-luggage only, the overhead lockers get packed with huge heavy cases that you really don't want to have fall on your head in the event of turbulence. Are those lockers really designed for that kind of loading, I wonder?"
Overthewing - Seriously have you flown EZY or FR ?
Ryanair have a 15kg carryon limit that they check - too heavy and its gets checked. Contrast this with the no weight carry on and you see pax on airlines asking for assistance to put them in the overheads......as a passenger if someone has a really heavy bulky case I refuse and suggest they check it. Cue abuse but I tell them if you can't lift it up then how you going to lift it down.