Those are legally binding information put out quarterly for the investors. They used to put out that information because the numbers looked good and it was extra publicity for the game. Wod put the subs below 4 mil hence they changed the tactic since ATVI as whole is still doing better (which is what investors want to know) with wow's dwindling numbers.
Wod and other exp "peaks" are irrelevant. Its the number of people who bought the expansion which says nothing about the actual retention when people play for a few months and see how dog shit it is.