See Mark Shuttleworth AMA: http://www.reddit.com/r/IAmA/comments/1j166z/hi_im_mark_shut...
I think you underestimate the echo chamber effect. The number of people who care about FOSS is minuscule, and marketing the Edge to that crowd would dilute the marketing message for everyone else.
I think you underestimate the appealing to as many disparate influential groups as possible effect.
/sarcasm
I never got the impression they had actually decided what hardware to use - eg it might have been Intel not ARM, as 4G on ARM SoCs is hard to get.
Comment quoted here for ease:
Although Ubuntu is a variant of the GNU operating system that I launched (see http://www.gnu.org/gnu/the-gnu-project.html), it has major ethical flaws: it contains software that is not free/libre (see http://www.gnu.org/philosophy/free-sw.html) and it spies on the user (see http://www.gnu.org/philosophy/ubuntu-spyware.html).
The Free Software Foundation challenged the developers of the Ubuntu Edge to design it so that it would run without user-restricting nonfree software, but they rejected that goal.
Dr Richard Stallman President, Free Software Foundation www.fsf.org www.gnu.org