I just found this:
viewtopic.php?t=9265. It is dated 2006. Seems to me this idea needs to be revisited.
Nothing in that thread mentions anything about teammates only being able to exchange adjacent territories, so maybe the idea was misinterpreted as teammates being able to give any territory they want to another teammate, which is a bad idea indeed. Only being able to give a teammate adjacent territories is not a bad idea, however, and it takes nothing away from the strategy of the game. On top of that, attacking an ally for a mutual advantage would never occur in actual life. Yes this is just a game, but the game does not have to be illogical.
One of the arguments in that thread was that being able to concede territories is unfair to the other team. That is a ridiculous argument because it all works the same way for every team. Sometimes you get the nice drop, sometimes the enemy will. If this is the main argument for rejecting conceding territories, then you may as well reject random drops too, because that's just as unfair. All advantages and disadvantages in this game are universal; everyone gets good drops, everyone gets bad drops, everyone gets good rolls, everyone gets bad rolls.
Strategy would be better suited being dedicated on how to eliminate the enemy rather than how to eliminate a teammate from your bonus area. Troops would be better spent attacking the enemy and claiming his territories than attacking your teammate.
I will say this though, there needs to be a limit or some measure taken to prevent a player from conceding all of his territories to a teammate thus allowing that teammate to eliminate him. Perhaps only allow two or three concessions per turn and allow no concessions when a player has less than ten territories or so.