Engine off or on?
I've seen a few assumptions that the engine was running. I saw nothing in the two articles that kd3pc posted that indicated that the engine was running and it certainly was not in gear. The articles say that the girl was attempting to climb out ... no doubt using the propeller as a step. I would bet that she slipped off the prop and her leg slid between the dual props (take a look at the dual prop configuation ... it's not hard to imagine how a small girl with a skinny leg could get impaled). If she had been attempting the climb out with the props in gear, her leg or foot would have been amputated by the props for sure.
My observations of Grady Whites (I've seen several on our lake) is that they are made for sport fishing and they are not designed for water sports. It sounds like it didn't have a swim platform, and come to think of it I don't think I've seen them with full-sized platforms. This sounds more like a case where the boat was being used for a purpose for which it is not designed. But there is nothing really uncommon about that.
Having grown thru my teens and early 20's with a ski boat with an outboard motor, I can tell you that I never got over that uneasy feeling that you get whenever somebody is behind the engine (or when you are in the water and the stern is pointed at you). In those days, only inboards had swim platforms and getting into the boat was a struggle for some people who couldn't lift themselves over the gunnel. Some people did resort to climbing in at the stern, using the prop as a step.
Since I've owned an inboard ski boat, I can tell you that you really have to work at it to get your feet near the prop because it is underneath the boat and the swim platform provides a fair amount of space. Of course reverse could get somebody in trouble, but for the most part, it is very easy to get real comfortable operating the boat with people in the water near the stern, especially in forward gear because the chance of getting any part of a human body (with a ski vest on) under the boat near the prop is pretty remote (unless you run a person over, of course). I am not saying this to justify operating a boat in an unsafe manner, I am just spelling it out the way it is. When pulling skiers on a routine basis, the engine is rarely shut off just because somebody is in the water near the stern. However, the gears are normally used with a lot of care.
Outboards and sterndrives are a different matter, though because the prop is behind the stern. I mention this because it appears that most people want to lump all matters of design and function together, when there really are distinct differences. Personally, I would never use a Grady White for water sports ... they aren't made for these activities. I see that a few models actually have a swim platform of sorts (but the prop is still exposed to anybody behind the boat) and they will advertise the boats for 'family fun' which includes tubing and other activities like that ... but they are designed for fishing and really have very little functionality for water sports.
Putting this accident in perspective ... there are so few prop-related accidents that it would be a shame if unknowledgable people had a hand in crafting and enforcing broad-brush regulation that unfailry penalizes boat designs that do not contribute to the problem.