Surely, the point is that 800 runners fall into one of two broad categories. There are the 400/800 guys and the 800/1500 guys. Giving an athlete in one category the training of an athlete in the other would not be to the advantage of the athlete. Several Olympic 800 champions have been high mileage trainers - Snell, Wottle, Ovett - but plenty haven't - Juantorena being the obvious example. Also WR holder Fiasconaro of Italy was another low mileage 400/800 guy.
In more general terms, the aim of any programme is to prepare the athlete for competition. If the athlete does not perform well in the important competitions the programme is a failure - no matter how impressive the training diary. Sometimes runners can forget that the aim is to compete well- not compile an impressive training diary. I know, I've been there!