OK, maybe I just don't understand it, which is completely possible. This is my Shiv (tri bike), running Reynolds AR80 wheels, which I believe are 21mm internal width, and a 25c tire.
Even so, I tend to run at least 90psi just to be safe. I don't necessarily run what the calculator recommends just because I do like a little softer ride, but I still maintain a minimum of 90psi to reduce the risk of pinch flats.
Part of the problem here is just the road conditions. Not so much the actual pavement, but the debris on the roads. There are very few dedicated bike lanes. What is marked as a bike lane is typically just a paved shoulder that often has whatever debris gets kicked up. I've had flats (mostly with tubes) due to auto tire steel belts and thorns from goat heads or mesquite trees most often. But I have had one or two impact flats from rocks. The rock they use before laying the pavement happens to be pretty much exactly like the rock that's IN the pavement, so it can be pretty difficult to distinguish at speed. And, of course, none of the rocks are flat or round. Oh no, they're perfectly tire flattening shaped, all big and jaggy sharp angles and s**t.