Growth of Yuwie not exponential

A lot of people are talking about the enormous and exponential growth of Yuwie. Of course it´s true that Alexa is showing a big growth of traffic for Yuwie:

But does the membership also has a similar growth? Is it really exponantial?
I decided to try and look up as much data about the membership count mentioned on different blogs on different dates, in order to be able to reconstruct the growth rate of the membership.
I managed to get quite some data, and this is how the chart looks like:

It's a steady (strong) growth, but not exponential (at least not for this date range).