If you become an expert in something, what you become an expert in depends greatly on personal interest. Some of that can definitely be "baked in" to your brain before you can do something about it.
But it's also true that you actually have to work at it to become expert. Duh. It's not like Tiger Woods just woke up one day with a phenomenal stroke... but it's also not like anybody can become Tiger Woods, even if they started young.
LATER: Okay, they kind of mention interest, or "motivation", towards the end, but nothing about how there may be a ceiling on accomplishment. This is pretty much a "duh", because of those people that are usually forgotten: the mentally retarded. Having relatives in special education, I've met some mentally retarded people, and there is definitely no way these people would be solving stochastic PDEs, say.
I think the research does point to the best way to achieve one's fullest potential, but it in no way proves that one can merely put more "effortful" study in and thus become an expert in any field. And they are somewhat ignoring the virtuous cycle of people being able to do something easier than others, an thus get an interest in that area compared to others, then work more at it, and thus it's easier... etc. Math was that way for me. I picked up math much more easily than other people at a young age, which made it easier for me to suck up even more math. I also had lots of opportunities other people, like my parents, didn't get. So I got farther, faster than my parents. But other subjects did not come as easily to me, and I didn't feel like putting extra effort in those to become "expertful". Kind of like the concept of comparative advantage.