Mudfoot, very interesting analysis. The completed turn is one of the signatures of "good skiing" and talked about all through this website as a fundamental answer to skiing well in: trees, bumps, crud, steeps, powder, and a better golf swing.
The round turn has been something promoted by the instructing world for several generations. They promote a safer more control ed descent of the mountain, but not necessarily slower look a good GS or SL racer. I contend they also reduce the accident/ injury rate among skiers. To see a skier hit a black bump run with completed turns, to me, is like watching a sports car ripping up winding road, it brings a smile.
Alas, here in the States we live in the time and land of NASCAR; this is what people pay a lot of money to go see. Crazy fast straight-a-ways, a minimum number of banked turns, and crashes they make a yard sale fall on skis look tame. Does this sound kind of like straight line skiing? This style of performance is what our society wants to see right now. Unfortunately you can not effectively teach that stuff in a ski school, the risk factor is just too high, but lawyer would love it.
The premise to this rant; maybe upper level lessons are less popular because of a cultural thing. The question; Mudfoot, are you a NASCAR fan?