I think it is important to remember, while this is instructive and has good pointers to the usability literature, it represents a particular point of view, not THE UNIX point of view of simplicity. In fact there is no one Unix point of view.
Some of original Unix authors are of a particular opinion, that Unix itself has gone wrong by becoming too complex. (see http://harmful.cat-v.org/cat-v/unix_prog_design.pdf, see also Rob Pike's critique of BSD sockets, etc.) If I were to summarize their apparent position on simplicity, it might be that the design should be structurally simple throughout, not just on the surface.
For contrast, note that ESR uses the X window system in his discussion of GUI interfaces. The X system was famously heavyweight and complex (at the time.) If I were to summarize ESR's apparent view of simplicity, it might be that simplicity is something you present to the user.
Some of original Unix authors are of a particular opinion, that Unix itself has gone wrong by becoming too complex. (see http://harmful.cat-v.org/cat-v/unix_prog_design.pdf, see also Rob Pike's critique of BSD sockets, etc.) If I were to summarize their apparent position on simplicity, it might be that the design should be structurally simple throughout, not just on the surface.
For contrast, note that ESR uses the X window system in his discussion of GUI interfaces. The X system was famously heavyweight and complex (at the time.) If I were to summarize ESR's apparent view of simplicity, it might be that simplicity is something you present to the user.