I agree with Simon. I've updated my site with the latest stats: http://wttruth.com/category-31-WT%20Publishers
The rate of increase has slowed, but it is still an increase. Even if this starts a decrease it would have to be a massive % to really affect their numbers. Currently it looks like it might start to decrease in the next 3-5 years, so they have time to do something about that.
They also have almost 2 Billion hours preaching with even less % converts per hour. If only they would spend that time serving the community doing real charity work (never going to happen, I know), they actually might start having some real growth. That in my opinion, is the only way they could grow at this stage. My old church tried door knocking 50+ years ago and they quickly caught on it didn't work. Through their charitable work I've seen many people come in through the doors from that.