Well, it's true that you can't win by resigning. However, at the higher levels of play, if both players have ample time, it's generally impossible that the player who is winning will blunder so badly as to jeopardize his win. Speaking about IM/GM games specifically, the worse off person will usually resign to conserve time for rest/preparation for the next game. If a player is down a piece for example, it's pointless to continue playing. I do however agree with your sentiment about resigning at lower levels of play.

EDIT: Oops sorry trusted them a little too much lol. This must have been one of those blind situations when he just resigned for no reason, or maybe the game was input incorrectly.