Have a look at the photos at
http://www.golfdigest.com/instructio...ingplane4.html
It does seem to me that the one-planer is reaching (i.e., arms not hanging naturally from the shoulders but angled out toward the ball) a bit more than the two-planer, although the two-planer seems to be reaching a bit more than I would consider kosher as well. Hardy doesn't mention this in the article, however.
Watching the Golf Channel a week or so ago, I noticed the swing of Stephanie Sparks, who was playing with the club pro at a place in Idaho. To my eye, her swing appeared to be a nearly perfect One Plane Swing, but I was struck by the extent to which she reached for the ball at address, so that there was very little angle between her arms and the club shaft.
I'm wondering how typical this reaching is of the One Plane Swing.
Note also in the pictures that the one-planer's club is not soled. The shaft is angled lower and the toe is up. Is this also part of the One Plane Swing setup? Hardy doesn't say in the article/excerpt. How could you hit with an iron this way? I think you can get away with it with a teed-up ball, but if an iron isn't soled properly I think there's likely to be trouble.
The extreme case would be Moe Norman, who took the One Plane Swing to its logical conclusion. He used a palm grip so that arms and shaft would be on the same plane as well. And he reached straight out for the ball.
So, is reaching a fundamental of the One Plane Swing or not?