Thanks shepherdless, interesting analysis. I'd also point out that the decrease in contributions may be larger than the decrease in income because of the important distinction between income and disposable income. In other words, while JW income may decrease by 3% in real terms, the fall in disposable income (which drives spending, including charitable donations) will be much larger.
The refusal to allow young JWs to get an education may really be coming back to bite Watchtower. Some small poetic justice I suppose. But hardly worth it for all the hardship it puts faithful JW born-ins through. Young JWs are splitting into various groups these days: 1) those who remain good JWs and stop at minimum education 2) those who somehow manage to excuse getting an education while remaining in "good standing", and 3) those who leave and pursue education as normal. As the years roll on, those in the first group probably have many occasions to observe others and wonder if they made the right choice.
So those who leave and get an education are no longer around and contributing to Watchtower, and those who remain have lower disposable incomes, and some may be increasingly resentful of the low income situation they were effectively coerced into, and less inclined to contribute the little they have. It's the perfect storm, or a downward spiral for Watchtower, to mix metaphors.