I have just read some postings from Moulton Avery dealing with this topic and the 1 - 10 - 1 "gimmick". Moulton makes excellent points that I do agree with. For a more in depth understanding I recommend everyone read that post if they haven't already. His arguments are more insightful to the paddler.
I only use the 1- 10 - 1 Principle as a means for demonstrating a simplistic understanding of the effects of cold water immersion. I am teaching this to persons that would be performing a rescue, already wearing appropriate thermal and safety gear and not persons needing rescue, not wearing thermal protection.
The problem with teaching something like this is that there are so many factors that affect the outcome. No 2 people will experience the effects of cold water immersion the same way. Those same 2 people could be affected differently under the same conditions on a different day. For example I could loose enough motor function of my hands and arms after only 5 minutes in the water and not be able to perform a self rescue. But on a different day under nearly the same conditions I might last 10 minutes. One degree or 2 in water temperature can also have a huge difference in effect. There are so many variables that can alter the outcome.
One big thing that Moulton writes about is testing your gear. I fully agree with this. Don your thermal underwear and put on that dry suit and get in the water. This hands on approach to experiencing the cold water conditions and how your gear will fare against it can enlighten a paddler greatly. A paddler may realize that they have been paddling for years in these conditions without adequate thermal underwear. This should help give the paddler a new found respect for the cold water conditions as well as an appreciation for their protective gear.
Life is a garden. Dig it.