Frank Pearce, Blizzard's EVP of Product Development, says he anticipates that changing very soon for several reasons. Eighteen-month-old expansion Wrath of the Lich King is not yet released in China, but when it is Blizzard expects to see good things: "...once we get that approval and launch Wrath in China then I think we will see growth." Cataclysm is on the way later this year as well, and Pearce says that it will probably bring "win-back" from former players.
Add that to the upcoming announcement of a new Blizzard MMO on the horizon, and the developers have high hopes for the future. You can check out the rest of what Pearce had to say over at vg247.