While I understand the choice...I'm confident Debian is more popular than OpenSUSE at this point in history, at least in every market we work in (web hosting, mostly). We have tens of thousands of installations (or 1+ million, if you count Webmin, but we have much less OS data for that). OpenSUSE installs can be counted on a couple of hands.
Historically it was pretty popular; SUSE may have even been the second most popular distro worldwide at one point...but, these days? Not so much.
I think choosing distros from slightly more diverse backgrounds makes sense. Ubuntu includes most Debianisms including dpkg / apt-get, CentOS includes most RedHatisms including rpm / yum, while openSUSE is a third way (that I know little about).
Replacing openSUSE with Debian wouldn't be sufficiently differentiated from Ubuntu, IMO.
The inclusion of something inheriting from Linux From Scratch might be warranted for didactic purposes - just for understanding what bits a Unix is made out of, fundamentally.
When I first clicked the link, I was hoping it would be something like Linux From Scratch. That however, would be a completely different class. More like math-for-future-mathematicians vs. math-for-future-engineers. I wonder if LFS could be adapted for EdX?
I think they just decided to go with the distributions that have a commercial backing behind them (or, at least, their "free" versions). But I agree that Debian should be on that list.
Most of the Ubuntu knowledge is likely transferable to Debian. Dame with CentOS and RHEL. I believe yast is a bit different than both RPM/DEB? I could be wrong.
Anyways, if those are the choices, they make sense to me
>The System Administration courses are written for CentOS 6, Ubuntu 12.04 LTS and OpenSUSE 12
(as the edX course should be the same as the course from the Linux Foundation, I'm assuming this applies as well).