Re: Rod grip style, and Lefty's principles
I'm going to make the assumption that Lefty advocated the thumb on top because this was all beginners. The probable reason being it helps to keep them from going back past 2 oclock. He has cast long enough to see a great many casters, some of which can cast better than Lefty, who use other grips on the rod.
I also assume that was the reason for the shelf thing. It's probably again so a beginner doesn't use his elbow like a fixed pivot point which will give you a dandy case of bad tailing loops.
Once people are not beginners and start to develope their own style, and everyone does, the shelf and thumb deal Lefty is talking about can be disregarded. I see why he says it, but if you are not comfortable, don't do it. A sure way to louse up your casting is make it uncomfortable.