[Al_The_Man]

then does that mean that it's up to the drives to control the feedback loop?

Pretty much in a nut shell, parallel port systems, Mach for e.g. do not close the loop in the control like say a dedicated motion card or one of the major CNC systems, they issue the command out of the port and it is up to the individual controllers to issue or keep track of each servo.
With true closed loop you can institute electronic gearing used in helical milling and threading, or servo slaveing.
and also monitor following error etc.
I have not investigated the Mach venture into integrating the Galil (closed loop) motion card yet.
Al.