I never understood the stepping into an empty shaft, because AFAIK the outer doors are opened by the inside doors on the car. So they can't open on their own if the car isn't there. Might be possible on older elevators with manual doors?
There can be an open door to an empty shaft when the elevator is undergoing maintenance. This happens sometimes in the high-rise building where I work. Normally the area around the open shaft is blocked off with some kind of barrier during maintenance, but I suppose that the mechanics could forget to put up the barrier out of negligence or someone could disregard the barrier and walk past it. It's also possible that the people who fall into the shaft are the elevator mechanics themselves rather than passengers.
It's been a while and I'm not sure which list I had read. It may have actually just been a few incidents that struck me as easily preventable. I think they were mostly due to maintenance in progress or pushing against the doors.
Looking over this list[1], it's interesting how almost nobody in an elevator ever dies. The worst incidents tend to involve people or objects that are halfway into the elevator.
