of the few i've watched (and certainly not even a minor sampling of 41 million) i'd say about 1 in 10 is excellent, 2 good, 1 reasonable, and the rest abysmal.
Hmm, Dave from LearningDSLRVideo had issues with extreme random crashes while using Vegas Pro 10...., and he left it...
Anyway, as numbers for tutorials, not surprising. So far I know, this editing software is so popular for Videogamers who want to edit their recorded 'actions'.
Also, it's possible because it was used by one of famous gamer commentator, his followers and fans would like to follow him.