Briefly:
Seems to me they added complexity for the starboard manipulator arm when they didn't need it. Hence, they have more bugs (from duplicated code) that they can't find (because it isn't used). AirplaneRule squared. -- SunirShah
Wouldn't you have to go out of your way to design a side without an arm and a side with an arm, vs. two instances of a side that accommodates an arm?
Perhaps there were going to be two arms, then the budget got cut. The code worked, IfItAintBrokeDontFixIt.
Plus that was 70d technology. In the 21st century we have ... the Special Purpose Dextrous Manipulator - denizen of the SpaceStation? and perhaps soon-to-be-rescuer of the HubbleTelescope - see http://www.chron.com/cs/CDA/ssistory.mpl/front/2780175 (MD Robotics makes both the Canadarm and the Manipulator, which is 2-handed)
It's in case they have to land in Australia, where everything is reversed.