Gladwell himself admits 10,000 hours is rather arbitrary. The point is still important though, as far too many people start a new skill and are disheartened by their lack of ability before putting in serious practice.
It might seem obvious that practice is necessary for most skills, but people forget it all the time. For example, when I'm teaching people programming they're quick to think themselves failures when they see the giant gap between their abilities and my own. What they don't realize is that I've been doing it for over a decade and, in fact, was much worse than them at first. [0]
[0] In fact, I probably only did HTML for my first whole month of "programming." One major advantage of learning things as a kid is that there's no pressure to be good.