As well as the peer comment about Gladwell (10k hours is considered the point you've mastered a skill), it's also a far more honest metric about how much time you've spent actually programming.

Maybe you were writing code, make design choices and debugging 8 hours a day. Maybe you were primarily doing something else and only writing code for an hour a day. Who would be the better programmer? The first guy with one year of experience or the second guy with 7 years?

I personally would only measure my experience in years, because it's approaching 3 decades full-time in industry (plus an additional decade of cutting my teeth during school and university), but I can certainly see that earlier on in a career it's a useful metric in comparison to the 10,000 hours.