Here we go again...
Not true, though you are correct about the majority of commercial potato lines. They do not have the correct genetics to grow tubers off the stem. They have been bred to grow tubers only in one location, to make mechanical harvesting simple.
Durgan, all your experiment shows, is that the potatoes you tried this with do not have the trait needed. If you would like to retry this with a different variety of potato with this trait, I will see what I can do to have someone in Canada get some to you.
Regardless of this, I would agree with you, that to date, with the majority of varieties of potato, it is fairly conclusive that it is unrealistic to expect a more favorite yield in ANY container, compared to growing a potato in the ground. Perhaps that may someday change with further breeding, and selection in TPS growouts bred for container growth. Growing in the ground will nearly always give you a higher yield, especially if you are amending your soils and fertilizing in a similar method to what Durgan uses.
See these two posts for my documentation on a 35" tall bin with Papa Chonca, a chilean landrace potato.
http://tomatoville.com/showthread.php?t=30203&page=3
http://tomatoville.com/showthread.php?t=33584
Video documentation of the reveal is in these video links I uploaded to youtube last year.
Part 1
Part 2
Part 3
Part 4
Part 5
Edit/Addition:
I am growing two different varieties this year, but have not documented them as well. Too busy with other projects.
2013 varieties grown in bins were 'Purple Peruvian' and 'Purple Viking'. PP yield was mediocre, PV yield was terrible. PV set potatoes all in a single location.
2014 varieties grown in bins were "CIP396286-7' and 'Papa Chonca'. Both grew, but yields were lower than when grown in the ground.
2015 varieties currently being grown in bins are 'Doty Todd' and 'Big Dog'