I usually never disagree with what the esteemed Mr. Lappos says, but in this case, I think he might be slightly off-base.
We tend to think of helicopter rotors as being absolutely and repeatedly predictable in their behaviour, much like the plank of an airplane is. However, when it comes to what is going on within a rotor system in flight, things get less precise. Ray Prouty has published charts in Rotor&Wing Magazine which show the data points to be all over the place, with a line more or less arbitrarily drawn through them at an "average" to give us a baseline for predicting performance. But what this tells us is that there are many variables - perhaps an infinite amount - which affect the way a particular rotor (or indeed, individual blade) will perform at any given time.
When it comes to VRS or SWP, we tend to focus solely on rate-of-descent of the aircraft, as if it were independant of other factors. Well, the air moves too, eh what? And sometimes that air moves vertically, not just horizontally. Suppose a helicopter developed a small ROD just as it encountered a slight updraft. The net result would be an increase in effective ROD, which might or might not be noticeable unless we were studiously watching the VSI, a gauge not known to be in our instrument scan during hovering ops (mine wags up and down considerably in a OGE hover). Therefore, I personally believe that making declarative statements like: "A UH-60 needs a ROD of 2500 feet before it can ever get into VRS" is the height of irresponsibility. Bollocks! I propose that in addition to the "hard" numbers that we know will aggravate or excite VRS, there are other factors which are quite nebulous that figure into the equation.
Did that UH-60 crew on Mt. Hood get into VRS? Who can know for sure? Even if the charts said (which we usually translate into "prove") that the aircraft should have been capable of the job, perhaps the rotor was closer to the "edge" than we know. Perhaps the rotor's reserve of lift at that HOGE altitude was borderline, and perhaps they experienced just enough of an updraft [in the mountains? come on, mate!] to cause them to fall off the bubble and into incipient (maybe not full-blown) VRS.
Then again, it appeared that they were hovering nose-in toward the slope. Is this true? Maybe I didn't see the whole accident sequence. Why not turn ninety-degrees to the slope? Would that not have given them better visual cues? And would that not have given them an easier "out" of they needed to lower the collective and bail from the situation for any reason? I wasn't there, but I sure wouldn't want to try to hold a stationary hover with a wall of white filling my windscreen.
Contrary to popular belief, gradual engine failures in a twin-engine helicopter do not cause a similar yaw-snap to the right (Yank birds) as they do in a single. As one engine falls off, the other goes to full power or beyond to take up the slack. We do not see any evidence of a catastrophic engine failure from the video (smoke, flame, etc), so I would move away from that line of thinking. Although the extreme coning of the blades does indicate (to me, at least) a reduction in MR rpm - or perhaps a over-application of collective pitch. Whatever DID happen, I believe it to be aerodynamic in nature and not mechanical - we'll soon find out.
Finally, Nick surmises that the Canadian Sea King at that airshow did not get into a setting-with-power situation, but rather a settling-with-too-little-power, owing exlusively to the right-yaw of the nose as the ship came down. Well, old boy, you're entitled to your opinion. I propose that it was indeed SWP (VRS), judging by the incredible rate-of-descent that built up so quickly, and the extreme coning of the blades as the poor pilot yanked everything he had to stop it, to no avail. The right-hand yaw was simply either his failure to fully mash the left pedal all the way (focused as he was on other, more pressing things in that brief second of time he had between "stable hover" and "Crikey, that hurt!"), or the inability of the tail rotor to hold the nose straight with the collective lever on the up-stop.
It is a myth to think that VRS is "hard" to get into, or that it must be excited deliberately. Anyone who would make such foolish statements has obviously never gotten into it inadvertently in the real world. Those of us who have know that all the "hard" numbers in the world don't mean a thing when the bottom falls out when you least expect it. Anytime you're in a HOGE situation you are susceptible, chaps.