First of all your question is totally legit. The way I view domain values is not by how much they cost, but by how much they save.
dmz happens to be a very desired term. Just google dmz very wpy for example and I think you'll get your answer. Three letters or not is not the question. It's what the three letters stand for.
If you are an organization that would like to build a web site about dmz technology, and I don't want to go into too many details but there are many ideas on the subject, and your choices were thedmzgroup.org or dmg.org, then dmz.org can probably cut your marketing budget by 1/10 as brand recognition and ease of message delivery would be significantly easier and cheaper.
For an organization like that, dmz.org is worth gold, while for someone who trades domains back and froth it maybe worthless. One's person trash is another person's fortune.
I'll conclude with the fact that all the domains we ever purchased were ones that we saw as a potential business, and I can go to many examples. We had planned and still may one day develop a project around a dmz technology. If we still own the domain it will be valid. If we don't, there is no chance we will do it. So yes, the domain is very valuable, very high commodity term, and can be a make or break for anyone interested in developing a business around the dmz concept.
Thanks for your questions!
Ed