When I was doing my TRI in Germany, we were 5 captains. I was the only one who knew, that 3ple hydraulic means mechanical back up.
From the FCOM1
The flight controls are electrically or mechanically controlled as follows :
Pitch axis
Elevator = Electrical
Stabilizer = Electrical for normal or alternate control. Mechanical for manual trim
control
Roll axis
Ailerons = Electrical
Spoilers = Electrical
Yaw axis
Rudder = Mechanical, however control for yaw damping, turn coordination and trim
is electrical.
Speed brakes
Speed brakes = Electrical
Note: All surfaces are hydraulically actuated.
The mechanical backups provide direct control of the hydraulic actuators on the rudder and the stabaliser in the event of loss of electrical control of the actuator. No hydraulics means you can mechanically link all you want you won't be able to move the controls.