I'd also like to see them do the same experiment but with higher hydration in the bread flour so he can determine if the quality of the bread is different if he treats the grain right. Also, he said in the long and boring parts he just did 90-minute proofs for both doughs, rather than going with the condition of the dough, and I think that could account for the denser bread flour result.
Finally, his AP flour dough was really sticky. I usually use 60% hydration, like he did for this experiment, but my dough never stays that sticky. It made me wonder if he weighed his ingredients accurately.
I have actually done the cheap flour vs fancy mill flour (not Shipton). Well, by that, I mean I made a few loaves of bread using AP flour from the local garage shop, and then just as we ran out of that flour our fancy mill flour arrived and I made bread with that, using the same ratios. I could instantly smell and taste a difference. The result was just "breadier" (in a good way). To me it does make a difference. I was perfectly happy with my all-purpose flour loaves when that's what we had. But then the new flour bread made me go, "Oh, yeah! This is good bread!"