You need to gather data over a longer time frame to be accurate. Not every active player is online at all times. The only person who can really provide that information is Badspot since he has control over the master server and knows who logs on and how often.
I would highly doubt there is more than 4000 active players on blockland, honestly though, smaller communities seem to be more friendly (hah) and creative. I doubt blockland would be bearable if it had a higher active count