These are based on games sales. Twilight Princess would not be very high on the list, because it only came out in December.

Also as a note, there are some listings you will see with 2 numbers, i.e.
35.) Kingdom Hearts II (PS2) - 391,544 | 1,129,196
These represent games that came out before 2006. In this case, Kingdom Hearts 2 sold 391,544 units in 2006, and 1,129,196 units in total since it was released.