It's more of a mentality thing for me. When someone says the defense played well enough to win the game when the game was lost, that seemingly excuses any mistakes the defense may have made, even if they played relatively well. One side of the ball or the other could have always played better than they did to ensure victory. That statement makes it sound like the defense doesn't have to improve at all because they did their job. Well they didn't do their job. Their job is to win the game, and they failed at that task.