Ok, 800,000 members signed up to the site.
A lot of members quit the site soon after joining.
A lot of members still play, but have been away for a while for one reason or another.
A lot of members only play live chess.
A lot of members only use the blogging/forum facilities.
Some (titled) members are just here to make the articles/videos.
That probably adds up to around 700,000+ players.
Great, thank you for that.
I was thinking of all those reasons, but I still thought that 800,000 was a huge number. Thanks anyway for clearing it up for me. 
Also, keep in mind that the "Daily Rank" numbers don't include members who are here every day, active on the site, but only play Live Chess.
I'm curious. Why does it say on the home page that there are over 800,000 members, but in the 'Today's Rank' section on 'My Online Chess' it says that there are approximately 77,000? It's a bit unlikely that there are more than 700,000 inactive players, right? Just wondering.
You can get a better idea of the membership by looking at the list of members "Most recently online".
Approximately 582,000 members have been online in the last 12 months.
Approximately 358,000 members have been online in the last 6 months.
Approximately 228,000 members have been online in the last 3 months.
Approximately 125,000 members have been online in the last month.
I'm curious. Why does it say on the home page that there are over 800,000 members, but in the 'Today's Rank' section on 'My Online Chess' it says that there are approximately 77,000? It's a bit unlikely that there are more than 700,000 inactive players, right? Just wondering.