The turn-off-the-phone crowd tend to be in situations where parents, young kids, doctors, interview calls, etc. getting in touch isn't a priority. Yes, voicemail is a partial answer but an imperfect one in this day and age. Didn't even used to have and just got messages on a voicemail device (after the mid-80s or so) but there's a much greater expectation of being able to reach people easily today.