Perhaps it is that other plants don't overgrow these areas with shallow soil because there is little room for deep root growth and higher nutrients in the soil?
One must be very careful to draw conclusions. I have heard from a number of growers that used an alkaline mix for N. northiana and had horrible results but when they transplanted to an acidic peat based mix the plants turned around overnight.
If I recall correctly N. clipeata grows on granite cliffs?
This is not to say that one shouldn't experiment. Often what works best for one person may not work best for everyone else. My goal however is to grow them better than in the wild! So trying to duplicate nature while a good starting point is just that, a starting point. A plant in a pot in a greenhouse is a very different situation than a plant in the wild. I wouldn't be half surprised if I brought buckets of potting mix dug from the wild where various species are growing, to find the plants died rather quickly potted in the wild soils.