Maybe some inactive members, who have never really been online, and have less than 5 posts were just deleted.
I haven't heard anything from the mods, but that sounds the most likely, the most inactive members just got their accounts deleted. Space wasters perhaps?
Yeah, it must be because of the clean up that the mods talked about in the "500 members" thread. Deleting the numerous member accounts from persistent types like Curry-Chicken!