It is highly likely to me that people who are successful in an area have spent significant amounts of time engrossed in all/most/many aspects of that area - for instance, music could include listening to music, playing music, creating music, talking about music, and so on.
However, for all those that are super successful in their area of choice and passion, I do believe there are many who have spent similar amounts of time invested in the same activities who haven't "made it big," become well-respected experts or bastions of knowledge in the area, who haven't gotten jobs related to those skills, who in short have failed to achieve much beyond thorough competency in the area. I think this is the result of many things - luck, connections, opportunity, as well as drive, passion, commitment, and probably a sackful of other qualities. It strikes me that a musician who does not know why what he does musically works, but only knows that it does, does not have the same ability to manipulate sound as the musician who knows exactly why a given chord progression is so powerful and elicits certain emotions.
I think one of my issues with the 10,000 hour rule is that it seems to encourage the idea that if you simply put in enough time, you'll be good. The thing is there is much more than that to becoming a true expert. I do not believe anyone can attain mastery without at least some natural gift as well as an education, but I do believe that someone with moderate talent who has to work very hard to learn his or her craft can beat out those with significant talent but an inconsistent, lazy, entitled, or half-hearted approach. You need to put in more than time. You need to come to the scenario with more tools than simply "lots of time" in your arsenal. And there are people who deserve to make it big, who have put that time in and more, who don't - or at least, haven't yet - for all sorts of factors.
I find both the 10,000 hour rule, and Gladwell's core assertion in Blink, ("think less, make better choices") at their core simplistic and yes, offensive. They both seem to encourage a certain taking of things for granted. They both dismiss effort, although in different ways. The message I get from Gladwell is that success really is as simple as 10,000 hours and the best decisions really are as simple as going with your gut reaction. I really don't like those.
If those are such truisms, what are you supposed to say to all those people who toil away in an area, put in their 10k hours and more, and never make it? What about people who know their gut reactions aren't healthy or helpful? In distilling concepts Gladwell throws nuance to the wind and implies that if what he suggests doesn't work for you, that you must be a failure somehow.
And I just can't agree with a man who tells me to think less before I make a decision, and that decision will magically end up being better than the one I'd come to after 30 minutes' thought.