The reason WoW is losing subs is part business model and part age. There are a tone of new games coming out and that have come out in the past year. These games all have various business models that are better for players pockets than WoW. GW2 is B2P while games like TERA, SWTOR have gone F2P. Now i dont know any Eastern F2P mmo's but i would guess they are doing pretty well since most of WoW subs lost are from the East. That being said WoW is also not the best looking game and its art is also outdated. Alot of players leaving might be leaving because they dont like the graphic quality or the cartoony look.
I left WoW because of business model.