So judging by those numbers sales increased by 1.1mil after day 1 for BC for the first month, 1.2 mil for wrath, and 1.3 for cata. So seeing as how its been increasing by 100k per expansion we can expact that trend to continue or at least be in the same ball park with 1.4 mil for the first month of MoP.

So seeing as how MoP sales are the first week and not day like the others we can only guess that the number is somewhere around 2.3-2.6 mil which puts the monthly sales around 3.7-4mil. So what we see is that your looking at sales between BC and Wrath. Not a good thing.