The WT fills a specific niche: high-commitment, high-control, high-social cohesion. Each member gives up a lot to be a member: time, freedom, worldly relationships. In return they are part of a special "select" group that is very tight knit. The high levels of commitment demanded increases social pressure to conform and keeps everything together. It also eliminates free-loaders who would want to be part of a social group but don't put much back in. Everybody reinforces the faith of everyone else. Those who doubt and may mislead others are segregated and removed.
That's the best description I've ever read of this religion. I think you've summed it up perfectly, especially w/respect to being "part of a special select group that is very tight knit." That's it--that's the controlling factor as to why people join and stay, or at least , a significant one. High commitment=high conformity. I think that's also why we probably won't see a JW-lite version, where birthdays, etc. are allowed. As has been mentioned, that dilutes the brand, leading to feelings of reduced commitment and less special-ness.
That said, I'm not sure where they'll go next because, as has already been noted, they'll have to do something in the years to come. I have a family member in Bethel who said that smaller English congs are merging all over the place, that "it's the trend now," and this was confirmed by another family member visiting friends in Canada. Yet its the English speakers, along with members in other developed nations, such as Japan and England, etc., that bankroll this business. And those are the countries where growth is flatlining-- the math isn't terribly hard. What's worse is that of those actually coming in and staying in, the majority are women who, organizationally, are useless (in WT land).
My prediction? Well, guess, really. I suspect we'll see a retrenchment, a hardening of the standards, a swerve to even more control and conservatism as a reaction to mounting losses. I'd point to the heightened rhetoric against higher ed and even partaking in such innocuous celebrations as "Friendship Day" at school, along with the recent clamping down on women who are translating sign w/o a headcovering and the 2009 DC mantra on "Imminent!" And it'll probably go on for some years. The growth in foreign languages here in the US and in Canada, and exploding growth in SA and Africa will keep the WT ball rolling for some time and they might have to rely more on electronic versions just to save money.
Eventually, after the ranks begin to seriously dwindle and still no big A--and I'm projecting 20 to 30 years--maybe the GB will resort to JW 2.0 I'm hoping by then I won't give a sh*t.
Cheers, folks, and Happy Friday