In searching the internet, I came across an old but good Facebook note written by the Defense Commissary Agency. Lots of people have questions about the Commissary surcharge, and this is the place to find the answers. I think you'll like it. It is pretty interesting stuff.
In the interest of not accidentally stepping on any copyright toes, I'm not going to quote any of it here. Click on over, you don't even have to be on Facebook to see the note.