Unless I missed it (because I read quite rapidly all posts at once) I did not see any reference that maybe, just maybe, Joomla adoption is due to the fact that it runs on Linux.
Be aware that having 80% of world population is poor. Running whatever on Windows is expensive. So, economic laws may rule this Joomla choice.Downloads are not a good argument to sustain preference. Nor the number of members in a site.
***
I am following DNN since before the name change and started following Joomla last year. I see DNN evolving more rapidly.
Database providers are a strong appeal for both products. Joomla have not come up with a solution for other db than MySQL in two years. And it seems it will take one more.
Module choices in Joomla seem to be broader that in DNN. However, developing a module for Joomla is not as easy as in DNN. Abstraction of DB in DNN is better than in Joomla.
AJAX integration in DNN is coming up faster than in Joomla. Client experience while browsing a site is important.
Site administration is easier in DNN.
***
I think what DNN could be missing is ability to run in other operating systems. Although there are efforts in that direction with Grasshoper product, C# DNN, and Mono Project.
***
Argument ad-hominem is an argumentation mistake. Although highly effecticve in creating advocacy, denotes a lack to support one thesis.My virtual friends: do not try to make a point by flaming others.