Some runs are groomed with a high embankment on one side, 4-6 feet high sometimes, like they're trying to even out a double fall line by piling the snow up. I've always thought that if anyone slips off that edge at even a moderate speed, they're gonna bite a tree, hard, because there's no escape once you start down that embankment, unless you're really, really good. I'd be curious to know how those embankments factor into the tree-impact data.
If the snow on the run is more or less level with the snow in the trees, if one loses it near the edge of the trail, at least there's a fighting chance of avoiding a tree crash, but if one loses it at the edge of an embankment, it's almost a guaranteed quick trip to catastrophe.
It is quite different in areas where they get a lot of snow and you can ski on and off the marked trail without problem. In a lot of places in my part of the country, the snow on the trail gets packed down by the groomer, and although the snow may be level with that beside the trail, it is a lot harder. Skiing off the edge of such a trail causes your ski to sink, and you risk skiing under a submerged branch, or skiing back onto the trail your skis, a foot or so under the surface suddenly stop when they run into the hard snow and you don't (been there done that).
When I read these stories about skier deaths, I think, "There, but for the grace of God go I." I enjoy the thrill of speed, and although I'm not usually trying to ski faster, I'm not usually concerned with trying to ski any slower either; I try to make perfectly clean carved arc-2-arc turns with as much g-force. When I was a younger man and spent more time skiing steeper longer terrain I was definitely one of those skiers who would seek an adrenaline rush by skiing as fast as they could. Back in the days when I was a speed seeking skier, I would ski all the runs including the moguls at a resort just to say I had skied them and so I would know every run, but I would then choose the best available run or line to maximize my speed. All other things being equal, I would choose a smoother run than a mogul run. But if the only way to reach max speed had a section of moguls on it, I would ski that line, making up for lack of skill with strength and athletic ability. The reason the mogul runs are devoid of high speed skiers are that these skiers now have a better option.
Yes, the moguls will usually cause a beginner to fall before they reach warp speed, but if you look at the stats, it's typically an expert skier skiing fast, losing control and ending up hitting a tree. Removing all the groomed runs will not stop the 20-40 year old expert skier from skiing too fast, loosing control and smacking a tree.
I do not want to see groomed steep runs disappear; I still enjoy them, even though I now enjoy slow skiing in moguls too.
Skiing is a risky sport, and people easily become oblivious to the risk. Having skied hundreds of days at 50+ mph, it can seem very safe until something happens and your internal speedometer gets re-calibrated. I'm all in favour of reminding folks that, yeah, they could die doing this.