@Isaac, first, thanks for the various citations and comments: I have learnt a lot more from this discussion than from Mark Dubovoy's fleeting reference. But I am still puzzled as to what you think is outright _wrong_ about his comment: if anything, out of its sheer vagueness, it does not contradict your observation that the important thing is many hours of "deliberate practice", not just idle, unstructured activity (”one hour, repeated 10,000 times“, as the old cliché goes).
But never mind: getting the facts straight on the role of both "hours" and innate assets in achieving expertise is far more important than worrying about whether "someone is WRONG on the Internet" ---
http://xkcd.com/386/P. S. a version of Gresham's law comes to mind: in any sufficiently long photographic debate, people will eventually invoke Ansel Adams and/or Henri Cartier-Bresson.