Speculating regarding the number of active playing users isn't really constructive, as these estimates never take into account that through out the day some users log in and other users log out. The real number of accounts that play the game every week is into the tens of thousands, with bots and spammers really only being a small percentage of it.
that's an interesting figure. it's really not hard to believe either if you take into account the fact that just about every player has, at some point or another, quit and returned (even if in year long gaps).
the real number of active players probably shifts on a daily basis. take into account every variable of life imaginable: jobs, school, being broke, being busy, too wasted/hungover to play, interests in other games, time with friend/family/partner, etc, to name a few.
from reading posts and stuff, you could figure that on average one person is manning at least 2-4 accounts at a time. i usually run 2 vendors on one comp and 2 mains on a laptop. but there are days when all of us are just simply too lazy to set up a vend.. so *poof* suddenly "4 people disappear" but not really.
i kinda hopped off the "this game is going to die soon" train once i remembered that people still play simply for the love, and that new & old players alike are coming and going all the time.