It’s the same principle behind Feynman’s lecture “There’s Plenty of Room at the Bottom”, when he discussed nanotechnology in theory. Of course he couldn’t point to full examples of what he was talking about, but it was very valid to say that ‘if physics works the way we think it does, then these things should be quite possible to do’.
See also Eliezer’s post Is Molecular Nanotechnology “Scientific”? (also found at the wiki article you gave — that wiki’s really starting to shape up).