>the 10 year (or 10,000 hours) road to expertise Why is this figure being bandied about as though it were an actual scientific fact?
Because for many folks, myself included, the opinion of a genius such as Norvig is solid enough to be treated as scientific fact.
This sort of behavior is why, even among scientists, a generation often needs to die out before new ideas can be seriously evaluated. (http://en.wikipedia.org/wiki/The_Structure_of_Scientific_Rev...)