If you had revealed the stairs that way, but didn't know the path to them, you might be forced to walk a long way away from the stairs in order to get to them (imagine the level was like a large 'C', with the stairs at the other point of the C from you). Would you think you should take damage if you're walking 'away' in terms of sheer X-Y coordinates, but 'towards' in terms of finding a path to them?