There's a very big difference between an order and "orders". What they're really talking about is more colloquially "assignments". It's about the chain of command. A general can give an order to anyone under his command to get him some coffee. But a general isn't supposed to find a captain and tell him to take a certain hill. The general is supposed to tell his colonel, who tells the major, who tells the captain. As a general rule, you're only supposed to get orders from your immediate commanding officer and only give orders to those immediately under your command.Hassknecht said:Elder: Hey there Initiate whatwasyourname, bring me a coffee!
Initiate: No can do, Sir, the Chain That Binds does not allow me taking your direct orders.
Chain of command is there for several good reasons. It helps to prevent contradictory orders (i.e. general says one thing and major says another). Along those lines, it reinforces the authority of the individual commander of his immediate subordinates. It also keeps a certain distance between the higher ups and those they are directly ordering to do very dangerous things.
It wasn't made up for the BoS, but has been used in militaries for quite some time.
EDIT: The elder can give the courier or vault dweller direct orders because the courier/vault dweller is outside the chain of command. If the courier had been assigned to be under Paladin Hardin's command, then the elder would have to give Hardin the order.
EDIT2: Now that I think about it a bit more, I should really make it more clear. It's not as much about rank as the above might suggest. A general, for instance, might have a captain directly on his staff. That general would give orders directly to that captain. At the same time, it would be improper for a Colonel who isn't on the General's staff to give orders to that Captain.