Some captain's have very little interest in what goes on behind them at anytime and wouldnt trouble themselves to make a useful PA. Personally I think as a matter of courtesy a PA from the flight deck should be made. How anyone can say that passengers are not nervous if the aircraft makes a GA is difficult to understand. Many passengers are very nervous of flying and/or it may be their first flight. I just timed myself on the PA I would make and it took 20 seconds. If a professional public transport pilot cannot make a 20 second PA while posistioning from a GA he is probably not suitable for command. I had a thrust reverser partially deploy on TO and still managed to make a PA during our very brief circuit to land.