I didn't get the sense that he intended "10,000 hours" as a pseudo-scientific assertion of fact.
It's a useful poetic phrase to express the observation that mastery takes time. Sure you could call that a Captain Obvious observation. However he used it in opposition to the idea that great programmers can master a new language in a few weeks. Since that idea is so popular, its opposite apparently is not so obvious.
He mentions 10,000 hours once or twice, and uses the word "mastery." If you hadn't ever heard of Gladwell, you wouldn't even know he's making a reference to anything at all.
It's so frustrating to see "Science-style bullshit" taken as gospel by intelligent, creative, and usually critically thinking people.