They will also lose other subscriptions because of the game-shop .Blizzard can do whatever the hell they damn please at the end of the day. They are going to do the in game shop to replace the lost income from subs. Business 101 and you don't know it :P
Their business 101 is a just a bet they will sell enough helmets to compensate for the money they won't get from those subscriptions and expansions sold.
I am not sure that this is a good bussines plan .
Just compare what they offer versus what the conccurence offer .
[ Buy game+buy expansions+mothly fee+ microtranscations] versus Buy game or subscriptions or microtransactions
Their offer in this moment is just bad .