Ratty in addition to the practical theory I have above, think about the emotional....you see a lot of, "...my Dad handed me a roll of X to load in the Z camera and at that moment, I was hooked for life on X film....".

That is what we are talking about. Artistic tools like brushes, paints, film, etc., have this realm that it hard to quantify and just delegate to another entity....just my $0.02..