Being inactive would get them off the autotracker, but they would stay a member of the forum. I guess the list above gives us an idea of how many are "active".
It looks like 354 members have actually posted this year, and 2372 members have done some sort of activity (logged in). The rest must be lurking or have left us.
I would have thought the number of folks who have posted something this year would have been two or three times that amount...Interesting.