Does a more ergonomic and user friendly interface/device make the human brain work less?
ISO 9241, a standard covering ergonomics of human-computer interaction, defines in its subsection 9241-110, "Dialogue Principles", that the interface in information systems should be (among other things):


suitable for the task
facilitate learning
conform with user expectations
describe its own purpose and functioning


You could translate all this to:


  Don't make the user think too hard about what he has to do


Shneiderman, in his "Eight Golden Rules of Interface Design" and Nielsen in his "10 Usability Heuristics of User Interface Design" (also on Wikipedia), make this even more explicit:


Shneiderman, Rule 8: Reduce short-term memory load
Nielsen, Heuristic 6: Recognition rather than recall


Reducing cognitive load is part of the industry definition of usability. By that definition a usable product "makes the human brain work less".



Sources:


ISO 9241-110:2006 http://www.iso.org/iso/home/store/catalogue_tc/catalogue_detail.htm?csnumber=38009
Nielsen, J. (1994). Heuristic evaluation. In J. Nielsen &amp; R. L. Mack (Eds.), Usability Inspection Methods (pp. 25-64). New York: Wiley.
Shneiderman, B., &amp; Plaisant, C. (2010). Designing the User Interface: Strategies for Effective Human-Computer Interaction (5th ed.). Reading, MA: Addison-Wesley.