Am I missing somewhere where it says open format? It specifically states they are using Amazon web services... It might not be to everyones taste but there seems to be this never ending battle for "I wish they would open source it", "I wish they would make it more open", "I wish they would use the BSD licence instead of GPLv3" it just seems to never end..
It's pretty easy to run an instance for a few minutes while you rsync the whole thing wherever you want. We used AMIs mostly because we ran the CTF itself in AWS and didn't have a great place to store the images otherwise.
Thanks for putting this on and leading me to smashthestack.org, I had looked (admittedly, a shallow look) for a CTF style game after doing one at a conference last year. These things are crazy addictive to me..