Why is it called "STBY RUD" on a Boeing 737? (Source: b737.org.uk)

Anyone knows why "STBY RUD" is named "STBY RUD" when the selection of the switch position activates the standby hydraulic system as well as the standby rudder system (by opening  rudder shutoff valve)? Is it because the standby rudder is more important than the standby hydraulic system as a standby system?
According to the Boeing 737 Flight Crew Operation Manual, the "Standby Hydraulic System" only powers the following:


thrust reversers
rudder
leading edge flaps and slats (extend only)
standby yaw damper


It does not power, for example, brakes, ailerons, spoilers and the landing gear.

I speculate that the word is chosen to remind pilots that the system powers the rudder but not other primary flight controls.