Having another look at the submission lists, I think what's actually happening is that the GOTMs are getting vastly more entries than the WOTMs, presumably reflecting fewer people owning Warlords. A month ago when I started this thread, that fact was temporarily disguised by a lower then normal number of entries for GOTM11 (I'm guessing, because of the highlands map taking longer to play) and a higher than normal number of entries for WOTM01 (I'm guessing, because it was the first ever WOTM). With submissions closed, GOTM12 has attracted 189 entries, almost exactly the same number as for GOTMs 9 and 10.
I'm intrigued that the SGOTM stats have turned out differently, with almost equal numbers of warlords and vanilla entries for SGOTM03 (for which people can choose to play either version). My guess is that the difference arises because the SGOTMs require greater commitment and therefore perhaps attract the - umm, shall we say, more 'dedicated' civ geeks, who are the people most likely to own Warlords.