Don't put too much stock in the photos as they are mainly for comparative purposes and, although I try to get them close, they aren't exactly the same as what you would have seen. As you noted the amount of light pollution will affect the "usable throw" per your definition, in addition to things like atmospheric conditions, your own eyesight, familiarity with the subject or contrasting (or not) backgrounds. I don't think there is a single set distance but if there is some sort of standard I'm sure someone will set me straight.
I can say that last night (45 degrees Fahrenheit, 80% humidity, light misting rain and the light pollution shown in the photo), I would be able to easily identify someone I am familiar with if they were sitting on that swing at 40 yards. For unfamiliar subjects I would be able to determine what they are wearing and their general description (estimated height, weight, etc).
At 60 yards I would be able to tell the difference between an adult and a child but I doubt I would recognize my own mother at that distance.