Tom, I would like to point out that choosing a climbing system is based not just on function but personal preference as well. Earlier you said something about how arborists are the only ones in the "working-rope world" to use as dynamic climbing rope system (in the sense that the rope moves). Part of this has to do with the fact that arborists start at the bottom and work up, rather than the other way around and that branches facilitate Ddrt in a way that few other climbing situations can. At the same time, in the recreation department i believe that rock climbing still utilizes a similar rope system for belays.
What I'm getting at is Ddrt has an established reputation as a useful method, both in tree and rock climbing. I don't like to use the banal saying "its like apples and oranges", but along those lines, a more fitting comparison (especially in the world of recreation) is skiing and snowboarding. Both are means of getting down a snow covered slope, but people usually prefer one over way the other because of certain subtleties. For instance, if your going for pure speed or moguls, skiing is the way to go. In the same sense, SRT gets you straight up the tree and for long ascents its definitely the way to go. But lets say you like to stop and hit every jump you can find or go to the half-pipe, then you're probably going to be snowboarding. Similarly, when climbing Ddrt, you can ascend a little, descend a little, quickly go up a little more and then drop to the ground without ever having to change even one piece of the climbing system. With skiing you have more gear (poles) and snowboarding is considered easier to learn. And a person can Ddrt without special ascending gear and its easier to learn. Then you got telemarking, which is like double footlocking long ascents. You see dudes doing it and wonder if they enjoy punishing themselves (just kidding).
Outside this comparison, there are other reasons a person might prefer Ddrt over SRT. For instance, if the tree is short and how low-lying limbs, it would be asinine to spend the time rigging up an SRT system to climb 20 feet. And some people simply like Ddrt climbing. Personally, i like to footlock my rope, which isnt much of a possibility SRT. That being said, I like SRT when the application is appropriate.