I have heard the same thing, but it seems like an urban rumor, at least as far as succulents go, because I have never unwound (or cut) a succulent's roots except under very special circumstances. There's some discussion about this in the sticky about repotting succulents.
One thing about drought tolerant plants is their roots seem to be really good at finding their own way. They often grow in confined spaces (eg. cracks in the rock) in nature, and their survival (thus their existence) depends on their roots' ability to explore, anchor, and find water.
When I put succulents in the ground (usually for good), I don't disturb the root ball if I can avoid it, either. That said, I also do make a point of avoiding sharp transitions in substrate between the original soil and the soil that will surround it... for plants in the landscape, I make a mix of roughly half native soil, half succulent mix in the immediate vicinity of the plant, so its roots will not face a sharp transition from one to the other.
