Bob Wyman has some of his own speculations as to what might contribute to the numbers disparity that SLinsider is reporting.

SecondLife is free for people to
sign up, which makes it realistic for people to keep an account to
occassionally log in with. If you’re paying $15 a month for Wow, I
think you’d be more apt to jump in-world more often.

Along with this has come a rise in one-off users. People who log in for a specific event and then don’t come back.

You think it would be cool to hear a band or live interview or
attend some product launch so you make an account log in and don’t come
back until the next time something cool happens.

That being said, Linden Labs themselves had previously stated that
they’d done some satisfaction studies on frames per second that clients
were achieveing and had found that if a user had below 10 FPS, they’d
bail and not come back.

I like FPS as metric than network numbers alone
as it reflects how a 3d client deals with both packet loss and latency.

There was also a comment on the post that “there was nothing to do in SecondLife but talk”. It’s easy to see where people would get this impresion if they’re going in thinking there are going to be quests and non player characters lying around waiting to tell them to kill things. However, at this point I’m having a harder and harder time seeing how a new person would get that impression in the first place. SecondLife requires you to bring your creativity to the table.

To badly butcher a quote: “Ask not what SecondLife can make you do, as what you can make in SecondLife.”.