It's the lack of any safety rail on top level of OP's link house that gets me, though, am I seeing that right?? So possible fall straight from the top ? (Gulp)
We have open stairs, had one accident in 7 years, which was an 8yo guest child horsing around (in a jumping game with others) on the stairs; I was running over to say "Stop doing that on the stairs" when she fell; she was going to fall down them no matter what, railing or not.
She broke a tooth in the fall; It's really hard to say if she would have been less injured or even worse injured if we had had a rail; she easily could have been bashed around in several directions in her fall instead, I imagine cracked ribs. Or crashed over the top of the rail.