hehe i did a post a couple of days ago regarding the sad reality of the contest which was the number of active accounts that is less than everyone expected (i won't post it here as i don't want to promote it more).
My results were very similar to yours and if i may add a daily active account is considered every account that does at least one of the following :upvote,post,comment, transaction, reply
here is the catch. If you use autovoting services or curations trails it count as active even though you may be out for vacations :p for a month!
Yup, a lot of "activity" is automated, maybe most of it :/