I think there is also a sense of trust, in terms of users worrying that they have clicked the right buttons in the UI to enable silent mode, if they get it wron

I think there is also a sense of trust, in terms of users worrying that they have clicked the right buttons in the UI to enable silent mode, if they get it wrong, a phone goes off at a very problematic time. With the hardware switch it is a very definite on/off silent mode.