Even so, you can't argue that the growth is exponential by simply looking at the graph. It could just as well be polynomial. To conclude that it is exponential you need some kind of analysis, like "every user brings two, those bring two each etc".
I believe this article is referencing the the metaphor and the hyperbole of "Exponential Growth!!!"...not a mathematical treatment of growth rates.
That growth eventually slows is a very very simple point, but it's important to never forget. Maybe everybody is making this too complicated because Saul Griffith is supposed to be a 'genius' now?
