First of all, yes, an 800-3k guy can easily get by on 80 miles week. I think few will argue with you. So your examples of Gray, Wholhuter, Lagat, Webb, Spivey and Marsh are irrelevant because most would say you don't need more then that for those events. 80 a week is a lot of running, especially when you're running fast intense workouts.
So now we get to 3k, 5k and 10k. Well, Lagat's best times at 3k and 5k have come when he has raised his mileage, he is a genetic freak, and has years of injury free consistent training. I think its hard to compare his training with anyone else. Not a fair comparison.
Marsh ran 80... in 6 days (I believe) and ran an event where success is largely determined by how good a hurdler you are. On the flat surfaces, Marsh wasn't other worldly, meaning he wasn't a beast because of his speed and strength, but because of his technique, toughness, and excellence at a particular skill event.
Rupp, you missed the boat. Rupp AVERAGED 80 a week for a year. That means he had periods of 100+ in addition to periods of 50-60. I posted an example of a year's worth of Bob Kennedy's training and he was as high as 140 and into the 120s for a few months (along with Daniel Komen, Moses Kiptanui and others)... but guess what his yearly average was? Pretty close to 80. That's because when he raced over the summer, he dropped down to 40s and 50s. That kills your average.
Solinsky, Teg and Ritz... all high mileage. So the 4 of our 5 American born sub 13:00 guys... all run 100+ mile weeks. Our best American born 10k guys... all run over 100 mile weeks at their peak. Nearly every African distance runner (5k and up) who is worth their salt... 100+ mile weeks.
And as for Ryan Hall? He has YEARS of high mileage under his belt. Hall's first run was a 10 miler or something ridiculous and has been running well over 100 mile weeks for a long time. He has an insane liftetime base and THAT is why he can run 80-100 now (mind you in 6 days) and thrive.