I believe the sterile cockpit is mandatory by FAA regulations. Between pushback and 10,000 feet and 10,000 feet and docking in the other direction, there is to be absolutley no chatting in the cockpit. Only business talk. The idea is that this phase of the flight is so critical, that there must be no distraction. Especially due to the risk of missing an important command that could lead to collision or disaster.
The DC10 was the absolute worst for call chimes....installed in the armrest and easily pushed, on a typical flight it could be hit probably 40-100 times an hour by mistake (this is not an overstatement)- so I must confess that I have completely ignored the call chimes/lights on this airplane, and relied upon frequent walks up and down the aisle to attend to passenger needs. Ding, ding ding ding ding ding ding ding ding ding....
Obviously problems do not get fixed with time. Delta's new Boeing 767-400s have entertainment controlers located on the top of the armrest, despite the fact there are no personal tvs. Whenever a pax puts his or her elbow down, it inevitably smacks the FA call button.