Like the winter of 2007/2008. The reason is the general market.
At that time the Much expected and May launched LOTRO could not hold subscriptions and so there was an empty space between the next "WoW killers" coming in mid 2008 (Age of Conan and Warhammer). This winter there is nothing new either, so people were recruited or coming back for a winter passing in WoW.
I mentioned this in the now closed thread of Jaylocks "5.7 million subs"... btw
Subscriptions - like GC mentioned after leaving Blizzard - have very little to do with in game issues. They are more dependant on general MARKET settings.
A new expansion, free to play introductions, a new MMO or marketing the WoW products at the right time have MUCH more impact.
In this respect do not underestimate the upcoming long term influence of WoW's Hearthstone either.
Before the end of this quarter there will be the WoD beta along with pre purchases of the expansion along with a free lvl 90.
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As this thread is about the Conference call I would advise everyone to read the 11 page transcript of the event on Alpha and the financial spreadsheet on the ATVI website.
Just a few tips: Bobby Kotick devoted his few lines to the usual established products but he could hardly hide his enthousiasm on the moneytising system of Hearthstone and its prepared worldwide East-West launch.
If anyone asks what made the difference of the 100 million (!) + dollars between 2012 and 2013 in on line gaming, despite yearly lower WoW subs ... now you know the answer.
The few million (sic) closed beta players in HS already had a huge impact. Rest assured it will not be the last quarter.