"Can you clarify regarding your statement about the experiential differences between elite road runners and trail runners? Are your referring to machined pavement vs. trail? I'm not sure why backpackers apply here though, that is an entirely different activity altogether. Backpacking is hiking."
My primary thought was that the primary stress on the body running pavement is stress on connective tissue. Little variation in the stress makes overuse injuries the main concern, and the joint and supportive muscle strengthening which I (perhaps wrongly) see as the main virtue of minimal shoes does little to address road running injuries. Hence the articles references to marathon runners finding cushier shoes less fatiguing.
Trail running (and I agree that lumping hiking in here is problematic) features a softer surface and more importantly variation in stride length, foot placement, and cadence. This means that overuse injuries are less dominant, and strains to joints due to terrain variations are much more likely. Minimal shoes can provide enough cushion from the impact on the joints while still requiring ankles and knees to strengthen and work regularly through their full range of motion. Stronger supporting muscles for joints mean fewer strains and sprains, and thus happier, healthier, and perhaps faster runners.
All strictly speculation, of course.