A huge strength of the original HP9100A programmable calculator, http://archive.computerhistory.org/resources/text/HP/HP.9100..., was that ALL 3 rpn stack registers were visible AT ONCE ON THE CRT.

So he has resurrected the original blank slate engineer’s intent; Osborne realized that people would be uncomfortable “knowing” stuff was in hidden registers, as apparently a great deal of non-technical people are today, 52 years later.