That should really just be called the hours of practice theory- the 10,000 doesn't hold up to much scrutiny except for a few select cases. It's great if you want to write popular non-fiction though!
In some sense, yes. If you read this post of his though: http://calnewport.com/blog/2008/11/25/case-study-how-i-got-t... you get the sense that it's not only about brute forcing hours, but also spending those hours wisely. In the case of math, that was making sure he could understand and recreate every proof perfectly. This was probably a lot more effective than spending those hours, say, studying only problem sets or lecture notes.
The 10,000 hours theory though requires something called Deliberate Practice. The theory notes the difference between simply doing something a lot, versus doing something with the intent to get better, presumably with some form of feedback.
The 10,000 hours theory relates more to the human lifespan than any specific training method. If you can be really good at something at 25, then at most you had ~15 years * 52 weeks per year * ~40 hours a week of practice = ~30,000 hours. Now, change that to deliberate practice and your looking at around 10k hours. However, some things like go blow those numbers out of the water. You can focus your life on the game a 8 and still be improving at 50.
Well the Dan Plan is looking to show that it is about training. But I should also note that the theory isn't that you stop improving at 10,000 hours, but that's how many hours it takes to be an expert.
Maybe Go is an outlier. I don't know enough about the game. But I'd be surprised that someone who did 10k hours of deliberate practice wouldn't be pretty good by most metrics of the Go community.
Go is likely similar to certain parts of language acquisition and musical talent in that there's a critical period involved. If you wait until you're an adult to start, not even 20k hours under a great teacher will give you real mastery. AFIK, every top player started training as a child.
