Talking about mileage, everybody can have reason. But there is a big difference between an athlete ALREADY PEPARED for his specific training and an athlete that has to TRAIN HIMSELF FOR BEING ABLE TO TRAIN in pecific way.
For example, talking about African runners, we must not forget their life while young. James Kwalia, for example, lived in a village 8 km far from the school. From 6 to 16 years, he went every day to school, coming back home for lunch, then went again and came again. This is a volume of 32 km a day, for 10 years, 9 months per year.
When I began to coach Kwalia, I was surprised in seeing how much resistance he had, without running very long distances. But, when I used with him 1 hr 30 min, the pace was very fast, together with marathon runners. His structure is very muscular, and he doesn't seem an athlete talented for long distances. But his engine, on the contrary, is very resistant, and he has also the same attitudes of a long runner.
This fact is due to his "natural activity", a real training able to build the aerobic capacity.
Many years ago, also in western society young runners were prepared for beginning their training already starting from a high aerobic level. It was the case of Jim Ryun, Gerry Lindgren, Steve Prefontaine (speaking about american runners), but also of Carlos Lopes and Fernando Mamede (in Portugal) or Salvatore Antibo, Francesco Panetta, Alberto Cova, Franco Fava, Venanzio Ortis in Italy. How many runners were able to run fast in short time in GBR more than 30 years ago ? Do you remember the mentality and the preparation of Ron Hill, Ian Thompson, David Bedford, Brendan Foster, and of all the middle distance runners (like Seb, Ovett, Cram, Moorcroft, Robson, Hutchings and others till Rowland, the last at high level ?).
The difference was their preparation BEFORE STARTING THEIR OFFICIAL TRAINING.
Do you know how Antibo began his career ? He was already 17 years old, and never ran officially before. He lived in Altofonte, a small village near Palermo. In 1979, Gaspare Polizzi, coach of some of the best italian runners like Zarcone and D'Aleo (28:11), organized a race there for recruiting new runners. At the race competed also a runner in national team in steeple (Cinà , 8:34 PB). Antibo arrived directly from his school, running with normal shoes and blue-jeans. He won the race, beating Cinà with a strong sprint in the last 400m.
This means that the previous preparation was already important, and he was already aerobically prepared.
Now, in our countries is no more possible to find the same situation.
But this doesn't mean that we can skip the "aerobic period of building". It means that we must do now MORE volume than in the past, because in any case we have to build the bases that one time best runners had, and now nobody has.
So, don't look at the FINAL TRAINING of a champion : this type of training is, of sure, very different from what he did 10 years before, that is the real proposal for a beginner.
And don't forget that the young age is the best period for growing in all the personal qualities. This is true for general resistance, but also for cohordination, ability, technique. So, if is a mistake to forget long run good for preparing aerobic system, is a mistake too to forget exercises for the improvement of technique, general cohordinative activity and the development of every type of skill.