I see it like this, take a grown man running up the stairs at a good pace and poof, slip and fall up about the next three steps with the shins and knees and such vs falling down a few with just gravity. Id rather fall down.
Falling down, if done properly involves much more than just a few steps. It invovles most of the flight of steps, some tumbling, and banging your head on the floor or the wall when you reach the bottom....
I have definitely hurt myself more falling up the stairs than down. It seems to happen much faster and the impact greater. When falling down, I feel like I have more time to brace my fall