Now that you have just mentioned it, is there any instance where the comm loop is used to convey feedback data in a closed loop control setup ?
Terry:
Only when the system response is slow enough that the com loop can keep up and any missing data can be compensated for until comunications is reestablished
I would say not "compensated for until comunications is reestablished" but "can survive comunications totally down"

One aspect of "communications" is that 485 transcievers make excellent signal to wire interfaces. I have used 485 transcievers many time to carry non communications signals from a to b becuase of the excellent noise resistance.

Erik