Don't they prune roots and limbs at the same time?
I don't know about the timing, but they do prune both. My understanding, from the conversations mentioned, was that it was definitely
not a 1:1 ratio, though. There are considerations with each that are not analogous to the other. Makes sense to me. Despite the many things my arms and legs have in common, I wouldn't try to wipe my arse with my feet.
Perhaps you can whack off roots with the audacity with which many people hack the limbs off of trees, in the same ratios, and it will survive. Personally, I would expect some drastically different results from doing this. Picture an elm tree with four codominant stems, and four main roots below the flare. You could cut 90% off of each of the four stems, and being a weed, the elm tree would probably live another 60 years just to spite you. Cut 90% of the four main roots off, and my money would be betting on a rapid decline and imminent death.
However, I've never actually tried this. Who knows? I would mention that there are things you can do to a young plant that simply won't work on a mature tree. I should also mention that I've cut plenty of tree roots, from a single tree, in building fences and decks without the tree showing any ill effects. I think they're a lot tougher than some people think. But I'm pretty sure there's a limit to it, and many species probably won't survive a whole lot of that.
Kidding...
