I'm not saying that a piece of mail should only be delivering if an automated system can figure out where it goes. Clearly human interaction is sometimes necessary. However, there should be some limit to how much human interaction a piece of mail can require and still be delivered.

My guess is that since Iceland is a small, sparsely populated place, a mailman there can follow such a map without particular effort, especially if the location is part of his regular route. I just think "delivering to a map" should probably be in the "quaint thing they do in Iceland" category rather than the "expected from any good postal service" one.