I haven't disassembled one before, but perhaps the F-91W features a circuit with an especially easy to break out pin for the beeper, or perhaps it's already exp

I haven't disassembled one before, but perhaps the F-91W features a circuit with an especially easy to break out pin for the beeper, or perhaps it's already exposed in some vital way so as to allow easy access without much prep in the field? My personal guess as to popularity : volume. Those watches are everywhere.