Or 10.5 million copies a year. To tell the truth its pretty shocking how minecraft has taken off...the guy will probably end up making 100 million off the game. And if he sticks to iterating it, it might end up making over a billion over it's lifetime(say 40-50 years).
Which may seem like a huge number, until you remember that World of Warcraft is making close to a billion a year.
The reason the number looks that shockingly high, is because he is a one man show.
My guess is that he is going to end up using his new found fame/resources to start his own game development company.