The NFL has it right preventing any game from ending on a defensive penalty. This makes perfect sense. The defending team should not be able to take a penalty preventing a touchdown or other scoring opportunity at the end of the game.
The dummies at the NHL have yet to figure this one out. Suppose with 30 seconds left, a vivid scoring opportunity emerges, at which point the defenceman takes a two hander slash to the shins of the apparently ready goal scorer, denying the goal. What is the penalty then ? A 30 second or whatever man advantage. It makes zero sense. In fact, this status of the rules provides an incentive to the defending team to do just this. You would expect after 100 years, give or take, the Rules Committee would have thought of this. Apparently, not so much.
The rule should be amended to (1), at the every least, extend the game by the length of the penalty, or (2) even better, allow the referee to award in his discretion a penalty shot or (3) in a clear case of malfeasance, declare a goal. The last option seems excessive, true, and should be used sparingly and in glaring moments of unfairness, but the first two are very reasonable.