I guess the difference here is that I'm assuming that the "medium hard" running done by those mentioned above, probably does fall under the 80/20 category of hard running. In fact, I'm not even quite assuming. Based on some rough approximations of my max HR and HR data from runs, I bump into Matt Fitzgerald's "hard" zone of +92% of max HR during runs of say 10 miles, where I'm running in between half marathon and full marathon pace.
Again the other simple takeaway which I think you overlooked in your above post is that a major piece of this is that "What the typical runner perceives as easy is actually closer to moderate." Then the other part of the rule thumb/ training advice is to slow down your easy/recovery days so as to have higher quality hard days, with hard in no way implying "interval". You've simply assumed that's what "hard" implies, probably as a result of the same dogma that leads to the "easy" misconception.
I also don't think you fully understand "rule of thumb." A simple google search reveals that a rule of thumb is "a principle with broad application that is not intended to be strictly accurate or reliable for every situation." I will help you out here. What I think you wanted to say, and I agree, is that there is no "one size fits all" approach to training.