There are 12,390 congregations in the USA, according to the 2007 yearbook.
Many of the congregations I know may have 5 or 6 elders, but there may only be 1 or 2 MS, and those MS are often up in years, 60+ years old, men who may very well never become elders.
A tell-tale sign of trouble in the org is not only when elders start dropping out, but also when there are few 'future elders', for lack of a better word. There are not as many 20-something MS as there used to be, as far as I can tell. What shocks me more is that the elders I know are oblivious to the fact that there are no future elders in the congregation. I think they are so caught up in their paperwork, talk preparation, and just getting by in life that they pay little attention to what's really happening in the congregation.
I know one thing for sure - anybody trying to live on six bucks an hour washing windows isn't going to have much time for being an elder...