Your complaint seems to be that few people are logged on at any one time, but that's not necessary to use Wave. It isn't a very good IM system anyway, so it's pointless to try to use it that way.
I'm also a little surprised by the author's criticism of having no one logged on at the same time. In our limited application of it, the value is not exclusively in real time communication, but in a better organized (non-linear) communication timeline.