Very interesting.
I always found it hard hard to believe that so many artists of similar historical periods would all have 'savant' type abilities enabling such accuracy. Also, some of the painters mentioned were very prolific, and many of their paintings show little evidence of having to use 'CTRL-Z' - pointing to the use of technical aids rather than a process of gradual 'refinement'.
Funny, when I was attending 'Art' evening classes, I was told that my work displayed too much of my engineering drawing training - so it's nice to see some acknowledgment of the 'old masters' debt to technology, to balance the usual emphasis on art's conceptual dimension.
Also, lovely to see that despite his long stay in California, Mr.Hockney has still kept much of his Bradford accent - made me feel right at home when watching the videos!