The problem with those studies is that they analyzed successful experts. I want to see a study where they have everyone putting in thousands of hours of work. How many kids get into Juilliard every year, and how many achieve the same level as Yo Yo Ma? How many grad students are working their asses off at Caltech and MIT right now, and how many of those are actually going to produce some significant mathematical work? I don't doubt that ambition and effort are necessary, but of course some degree of talent must be key as well.