When one player has no chance of advancement and another has a chance contingent on winning that match, the "reward" for the lower ranked person to strive for is nothing more than mutually assured destruction. It strikes me as more sportsmanlike to concede.
More sportsmanlike for whom? The person who gets a free win and advances? Or the person in another match who has to play the game, only to have its results nullified because another player got a free win simply due to match ups?
Again, I think concessions under the right circumstances are ok. I just dont like having them couched in terms of being 'sportsmanlike,' because from the perspective of other people in the tournament a given concession could be anything but sportsmanlike.