If you fly very much in the back (I do all the time) then you will find that almost all international carriers are far more selective about when the seatbelt sign comes on. In fact I have been on flights, especially Lufthansa, where the 744 is being bumped around pretty hard and no light and no announcement. If you hear the Captain come on the PA and say he is turning on the seatbelt sign because they are expect turbulence coming up, boy you better buckle that belt because it is going to be rough.

I recall once on Lufthansa we were flying in a TS on a 737 headed into Graz, Austria and the cabin crew was up doing a meal service!!!

Anyway, my main point is that the US Carries are more than a little conservative with the use of the seatbelt sign and that only creates the issue of passengers ignoring it when it is on.

Having flown on many international carries, you are far more likely to buckle when they turn on the sign. Especially on LH.

For me, if I am sitting, then I am buckled. But on a 12 hour flight, I have to use the toilet and stand to stretch and that is just a chance you take when flying thru the air at 500mph in a mettle (soon to be plastic) tube