Just as everyone uses a light switch's toggle, and a volume control's knob and even the "Touch Pad" of the modern telephone; there needs to be a similarly SIMPLE interface to the computer.

It is that Gap, between the GUI and Assitive Technology that needs attention! 
For the time being, I'll call it the "Hardware User Interface," or HUI. 

Instead of less than 5% of the population availing themselves of the awesome potential of the Personal Computer, the GUI is now enabling greater than 50 percent of the population to become computer literate. 

This is a GOOD thing, no longer is the computer a novelty for a chosen few, it is now--combined with the Internet--a democratic Leveler/Equalizer for the average citizen. 

However, there is still a very large, and important remaining population that  seems unable to benefit from the GUI. 

Where the Virtual interface with icons and the mouse  might be intuitive for younger users,  this population requires a more basic intuitive interface approach; that is to say, something that we all use in everyday life; something as familiar as a light switch: flip it UP and the Program is "ON," Flip it Down and the Program is OFF." 

Similarly,  when a volume control KNOB is turned counter clockwise,  the sound is diminished, etc.  --You get the idea...

CLI   Command Line Interface 
        Use of Text as command inputs. 

GUI  Graphical User Interface 
        Use of Graphical Icons for Virtual command inputs. 

HUI  Hardware User Interface 
        Use of switches, knobs pushbuttons, etc. for command inputs. 

Assitive Technology
        Use of 'all of the above' & more, to communicate between the disabled 
        user and the computer.