One purely speculative theory of mine is this:
Berg was in Iraq with the comm tower non-job for cover-for-action to travel around odd places.
His real mission was to act as a messenger, trying to become a go-between from Int'l A.N.S.W.E.R. to Al Queda. I mean, ANSWER can't exactly just pick up a phone to call Al Queda. To communicate with them, you have to GO to where they ARE, and fish around dropping hints, until you're picked up.
That's when you tell them the glorious news: you have come from a group "allied in the struggle against the Western imperialists" yadda yadda. You have a message, and an offer to coordinate activities, or perhaps hints on how to tweak their operations for the best effect, IOW, what and when to pull an operation which will result in the defeat of George W. Bush in November.
You expect to be treated fairly well, perhaps roughed up like the fake Japanese hostages/peace activists. After all, you can't talk to Al Queda, and just walk away like nothing happened.
But they saw the Jewish name Berg, and the Israeli passport stamp, and that trumped his ANSWER credentials. When the AG Prison scandal hit the papers.... Nick went on to serve a higher Al Queda purpose: human sacrifice on film.
That's why Daddy Berg (Mr. ANSWER) said "They killed their best friend."
The above is pure speculation on my part.
I agree with much of what you said.
This was not a 100% random killing.