Well, it seems there is some unknown number of "core" players who have been sticking around since the earliest years, then there is this larger group that comes and goes in waves (often associated with new Raids, but also the try-and-drop types), and then there is the biggest group of subs, those based in China.
The Chinese numbers will continue to drop until the next Expac, simply because NetEase has stopped advertising this expansion (according to their own quarterly report, it seems games have a very limited shelf-life over there). The "waves" group will continue to decline as Blizzard has predicted, and the old-timer group will largely stay put.
We do know from Blizzard that the majority of WoW subs are located in China now, so that means a minimum of four million and one Chinese players. Beyond that, who knows what the actual number distribution is.
Chances are, a site like WI is attracting zero people in China, several hundred old-timers and a smattering of wave players who have discovered this site.
. . . Or people just lied in the survey and this is all a big circle jerk. Still more engaging than dailies, though!
Since someone else mentioned it, I started playing warcraft with the original game. Then WC2, and the expansion pack, which I beat on buying wow accounts horde side. But the alliance side, I just couldn't make any headway at the beginning of the last mission, which I think was where you actually destroy the portal itself. WC3 felt like a rehash of a better game and I wound up cheating through the last few missions. I don't remember if I even finished Frozen Throne.
For WoW itself, I tried the game either right before or right after Wrath launched and found it way too grindy, with way too little direction on what you were supposed to do. I wound up giving up with a 30ish warlock one because of the annoying boar spleen quests, but also because the friend that was getting me to play wouldn't actually play on a same level fast wow gold character. I came back soon after Cata launched because I wanted something to "do." I also had a coworker that was wanting me to be a paladin healer for his t11 raid group. That guild kind of fell apart, so I never got to pally heal, but my Mage seems okay with that.