A week or so ago, I had one IE7 'tab' open to the "Community" page just to monitor what was being displayed. I had another 'tab' open to the "Active Forum Topics" page. I would then open several other 'tabs' to the entries from the "Active Forum Topics" list to read them (and maybe respond).
Periodically I would refresh the "Community" page and I found that my online name would most of the time show me as being in "Home", and a few times as being in "Forums". Once or twice I remember being listed as in "Community", but often my name would not be in the list at all. It did not seem to matter what I did LAST before refreshing the "Community" page, the location listed for my name changed sometimes and my name sometimes just wasn't there at all.
I have assummed that there is some timeout on server accesses and if I take too long reading the several 'tabs' I have opened then the server deletes me from the list and does not add me back until I access something and maybe the "refresh" of the "Community" page sends me the data before the list actually gets updated to show that I am accessing the web site. But, there seems to be some sort of delay in updating the list, too... like maybe it is a low priority process and if the server is busy the list is not updated in a timely manner.
Maybe you are not seeing a lot of users on-line because some of us are being timed-out on accesses and thus don't show in the list even though we are actually active at the time????