jgnat, you're right on the money with your observation about the Watchtower doing the best in countries that have already been 'softened'up by other, more traditional variants of Bible-believers (most notably, the "churches of Christendom" to borrow the Watchtower's damning collective title for other groups espousing Christianity). There is one remarkable exception: Japan - although the Watchtower's heyday appears to now be over in that country. It is a country that rapidly incorporated Western ideas into its way of life, but Christianity - or more specifically, the Bible, is not a staple of the Japanese outlook on life.
cedars, I am sympathetic to slimboyfat's view that the Watchtower does not inflate its official publisher numbers. Some of those numbers it reports annually are plain embarrassing. Denmark, for example has hovered around (from memory) 13,000 JWs from the mid 1980s until the present day (nearly 30 years of stagnation!).
Plus, countries such as New Zealand show spurts of growth followed by stagnation and decreases. Hardly the result of doctored numbers. Some support for the view that the Watchtower does not doctor its numbers is seen in the steadily increasing total number of "anointed" - surely if they were manipulating the numbers to look good, they'd want these potentially easily doctored numbers to show a decrease, but for several consecutive reports, the nmubers have been going up and up, in contradiction to the Watchtower's claim that the anointed are dying and getting their heavenly reward.
Still, to say that I think the Watchtower provides honest, undoctored numbers of publishers does not rule it out from ever doing lying in its reports in the future. The rumblings are that fewer and fewer witnesses door-knock on a regular basis. That is, current JWs door-knock on average far less than earlier breeds of witnesses.
Besides, if any doctoring of numbers is going on, I'd suggest it is likely to be at the local level where the temptation to inflate one's field report must be perrenially tempting - and easily accomplished. Not that I ever, ever , ever did it; and nor did my pioneering buddies.