There are plenty of people that spent 10,000 hours studying math but due to mental limitations are far from experts. However, most people don't spend anywhere near that amount of time studying math unless there reasonably intelegent in the first place which suggests that the only validity to that number is the less gifted generally give up before wasting that much time.
What really makes math stand out is there are people who became recognized experts well before that magic 10,000 hour number. EX: Srinivasa Ramanujan http://en.wikipedia.org/wiki/Srinivasa_Ramanujan
Oh? He had almost no formal training, but that doesn't mean he didn't put a lot of work into it. How many hours do you think it took before he was a "recognized expert", or since this is Ramanujan, before he developed new theorems which would later be recognized as being that of an expert?
Quoting from the Wikipedia link: Ramanujan's introduction to formal mathematics began at age 10. He demonstrated a natural ability, and was given books on advanced trigonometry written by S. L. Loney that he mastered by the age of 12; he even discovered theorems of his own, and re-discovered Euler's identity independently. He demonstrated unusual mathematical skills at school, winning accolades and awards. By 17, Ramanujan had conducted his own mathematical research on Bernoulli numbers and the Euler–Mascheroni constant.
7 years at 4 hours per day = 10,000 hours.
Do you think he averaged less than two hours per day on math as a teenager? Based on what little I know about him, I don't think that's the case.
Also, your terminology is the core of the debate here. You say "the less gifted," but the debate is that there may be no "gift", but instead the dominate factor is the willingness of the person to go through a difficult learning method with delayed rewards, in order to become an expert.
I studied math, physics, and computer science as an undergraduate. I spent a lot of extra time learning and practicing software development, while I rarely did math and physics beyond what was needed for coursework. I believe most of my 'deliberate practice' went into CS. I'm now an expert in software development, especially as it relates to biomolecular structures. I firmly believe it is my interest in the topic and the lack of competition (meaning that it pays well) which led me here, and not some intrinsic gift.
What really makes math stand out is there are people who became recognized experts well before that magic 10,000 hour number. EX: Srinivasa Ramanujan http://en.wikipedia.org/wiki/Srinivasa_Ramanujan