Thanks Harald, that was a great reply, with lots of rich details about your thinking. And thanks, Max, for providing links to more of Harald's writing on this subject (I'd looked prior to posting my question, but didn't see those, probably b/c I'd searched Harald's posts for +stance +Ligety and +width +Ligety, instead of +stance +width). I would have written earlier to say thanks, but I wanted to take the time to digest this info.
From what Harald wrote, I gather/infer the following (the key point that alleviates my confusion is no. 3):
1) PMTS is based on WC ski technique, and WC SL technique in particular. The reason PMTS looks specifically at SL is not that PMTS is interested only in SL turns. Rather, WC SL technique contains all the basic mechanics needed for all types of turns, except it's not permuted (or as permuted) by the additional tactical and technique features that result from the extraordinary speeds seen in WC GS and speed events; such features are not functional for recreational skiing (or even for developing racers) and, more importantly, could compromise development were a learning skier to attempt to emulate them. [His answer goes into why this is the case.]
2) The free-skiing of WC GS specialists may therefore not be a good model for a recreational expert skiing at the same speed and turning radius, because the former may continue to use their in-course movement patterns even at recreational speeds.
3) It's not simply that there's one sort of transition stance width (TSW) for WC GS/SG/DH and another, much narrower one, for everything else. Rather, it's a continuum: there are significant benefits to a narrow TSW (better balance and facilitation of entry into the new turn), and thus the TSW should be as narrow as possible for the skier's expertise and for the forces being generated (with additional adjustments for conditions like moguls and powder). Therefore, as skill/speed/angles/turn radius increase, the TSW requirements are relaxed. Thus, for optimum TSW, we have: intermediate <= recreational expert making controlled slalom turns < recreational expert making fast GS turns on an empty slope < skilled USSA Master competing at the GS Nationals < WC GS competition (where "<" can mean "slightly less than" or "significantly less than"). Indeed, you could say that Ligety's GS TSW (except where he overdoes it) is PMTS, if PMTS were extended to that regime.
Max_501 wrote:And he's racing to win. Pushing himself to the max on every turn. We aren't going to see many picture perfect turns when a racer is in the course.
Just a minor point, but note that one of the nice things about this footage is that it's a training video. I like looking at training videos specifically because, while one still sees mistakes, the skiers are not (usually) at the hairy edge the way they would be in a race, which allows their native movement patterns to come through with less "noise." For that reason, I've tried locating training video of Hirsher in SL, but unfortunately have not found anything more recent than this CSCF/FESC footage from 2010:
http://www.youtube.com/watch?v=JuZJim10RXA . [If anyone has a link to newer material, that would be great....]