World of Warcraft: Cataclysm (PC) Sales 3.64M
World of Warcraft: Wrath of the Lich King (PC) 6.94 M
World of Warcraft: The Burning Crusade (PC) 7.42M
World of Warcraft (PC) 11.99 M
So looking at the sale numbers this means
4.57M Are still playing World of Warcraft
0.48M Are still playing The Burning Crusade
3.3M Are still playing Wrath of the Lich King
Also the numbers are for copies sold. So it does not count people that quit or were banned and in all fairness Cataclysm was not released in the eastern markets yet.
But The numbers do not add up do they?