I was looking at the new member stats. Those stats you are showing look correct but are not the ones I can see. Here is an excerpt.
The stats must be counting spam registrations.
Many hundreds of spam accounts get set up every day, but almost all of them get trapped by the spam filter and the accounts are not activated, but they are still accounts in the database. I go in manually and purge those every week or two (easy, just a few clicks to kill them all)
I have just enabled another spam trap and I think it's working, as I only have 46 members "awaiting approval", normally that would be a thousand by now.