User blog comment:Dopp/Technical Update: May 17, 2011/@comment-3080486-20110520135728/@comment-1656630-20110520215655

Yeah, about that. The original plan *was* to enable it for all wikis created after May 18th (2011) so that they could walk through the process from scratch (meaning the system would send out its first notifications in 14 days to inactive admins, reminding them to engage). However, the engineers realized this was a lame way to launch a system test. :) So they instead enabled it for all wikis that were created sine May 1st.  This means that if you made a wiki since then and haven't done anything on it, you are part of the group who received the first messages.