Call of Duty 4 hits over 14 million players

[Spire_VII]

From my understanding of how the article is worded, they mean that 10 million unique Xbox Live users have played the game in some form. That does not mean the game has sold 10 million, as people could have borrowed the game from a friend or rented it or bought it used (none of which ad to the total amount sold) and played it and were connected to Live.