These are decent rules of thumb, but they are just that - rules of thumb.
I was always been a quality over quantity guy. I would identify the mileage that I was going to run and then figured out how to get the best bang for my buck out of that mileage. As I have moved up in distances over time to the marathon, my perspective has changed a little. Instead of starting off with the question of "How many miles do I want to run?" I now start oft with the question of "What is the highest mileage that I think can hit?"
The answer to that latter question is based on a couple of factors: the amount of time and energy I expect to have available after attending to other obligations (family, work) and my best guess as to what I could handle without getting hurt (which is really a function of my prior running volume and my recent training loads).
As a guy who started running as a walk on as a college freshman, I rarely got much about 40 mpw as a college freshman despite being a 5000m guy. Hit 70 a couple of times as a junior, but got hurt as a result. For the most part, by my senior year, I was in the 45-55 mpw range running 5000m/10,000m and had a moderate degree of success in racing .
Similarly, when I ran my first marathon, I peaked at 80 miles as that was 10 mpw more than I had ever run, and 30 mpw more than I had run in nearly 2 decades. Second marathon I peaked at 100 (because I had a higher degree of confidence after the prior 80 peak), third at 90.(because 100 caused me to nearly burn out in the 2nd cycle).
The gut reaction is "well you would have had more success had you run more," but I honestly believe more miles would have meant a much higher injury risk which would have undermined my goals.
So you can be pretty serious about training, and can be really giving it your all, but still be well below your thresholds.