There's a slight illogicality about all this; it must surely depend on what department we are considering. If I have a late appointment at my GP surgery it can sometimes be delayed by as much as an hour - presumably because everybody, or almost everybody, who had an appointment that morning, turned up. Some things are difficult to estimate in terms of time. They can probably work out the duration of a mammogram appointment to within a couple of minutes, but GP appointments, while allocated a standard length of time, could take anything from a few minutes to over 20. Surely the cost of a missed appointment in those circumstances is negligible - receptionist time on the phone to make it in the first place, and what else? Even my notes are on a computer, accessed by the doctor immediately before I'm called in, unlike those at the hospital's eye clinic which are in a cardboard folder now an inch and a half thick. I'm sure I heard recently that hard-pressed GP surgeries actually rely on the probability of no-shows in order not to have to rush through the later appointments in order to fit them in.
This is not to deny the amount of time and resources wasted by those who can't be bothered to go, and at the very least, it's rude not to even let them know, but it's not a one-way street.