It's one of those articles again that uses data comparison in a way that allows you to prove anything you want.
They compare the revenues from april 2013 with september 2012. Small detail, they released an expansion in september 2012 ...
If WoW loses 1m subs when going from month A to month B, then the loss in subs is roughly 15m, without counting the amount of money those players would have spend on mounts/pets and transfers. That is not anywhere close to 54%,

It's purposely abusing data to purposely spread misinformation that this website did. No clue why. But yeh politicians and media do it everyday, so I guess it has become common practice.