Glynn, I agree with all your points, but I think you missed some other important assets of Ubuntu. And the ones that I most admire about it as a project.
The first one, is that everybody is welcome, it is a community of communities, GNOME and KDE people on the same place, server and desktop, enterprise and education, and recently multimedia people with Ubuntu Studio. They have achieved the goal of making everyone feel like they are at home, no matter what you know, no matter what you like, You Are Welcome, your words are going to be listen, there are no second class citizens.
And the second one, is the tools, launchpad, despite of being closed source, is probably the better set of community tools out there in terms of usability. You don’t need to know about gettext or svn to do collaborative translation, you don’t need to know the deep roots of the system and the organization to know how to file a bug, and more other things that make community life easier and more accessible to most people.
Community is growing around ubuntu, in part, because is a comfortable community to work with.
My two cents 🙂