Interesting insight about the direction of the spins. I had never heard or thought of this, but it seems to make biomechanical sense. Putting it crudely, the weight of the swinging leg tends to shift the balance in the spinning foot onto the ball going forward or onto the heeling heading backward.
As for your future post about the origin of power and the waist, I am looking anxiously forward to it, since I had a similar idea. I am somewhat confused as to whether the waist is supposed to guide, control, lead, or generate power, concepts which do not necessarily imply the same physical movements. Adhering the qi to the spine is another concept that seems related to this, but which I have difficulty making consistent with other statements of principle.
I think the classic statements about this more or less talk about power being "rooted" in the feet and being "guided" or "led" by the waist, "formed" or expressed in the fingers, etc., all under the command of the mind. On the other hand, everyone seems to talk about the waist as being the origin of movement. For instance, if I can recall correctly (an iffy proposition), Yang Zhen Duo talks about the waist "carrying" or "bringing" (dai4?) the foot around, when he describes turning a foot in or out. Perhaps Jerry or Louis could clarify the terms generally used and the implications.
As for other ideas about where movement originates, in Jou Tsung Hwa's Tao of T'ai-Chi Chuan, he describes the first Chen routine as having the body lead (or move?) the hands (yi3 shen1 yun4 shou3), but the second routine as having the hands lead (or move?) the body (yi shou yun shen). Not being a Chen stylist, I have always found this a little bit mysterious and hard to square with my instruction of using the waist to "move" everything. However, I have encountered similar statements elsewhere and so repeat it here, in case someone else can explain the "complete" theory of T'ai Chi movement.