The feedback and shut-off solenoids are not the same and have different functions. The shut-off solenoid cuts fuel to the idle circuit at engine shut-off to prevent dieseling and during extended deceleration periods to save fuel. Under other conditions, it stays open allowing fuel flow.
The internal feedback solenoid operates at rpms greater than idle speeds. The computer drives its on/off duty cycle based on inputs from the oxygen, TPS and vehicle speed sensors, to name a few. Its purpose is to maximize fuel economy under steady, low to medium demand driving conditions.
For more info about the solenoids and the idle and primary circuits, look at the guide included in post #8 of this thread:

http://www.mightyram50.net/vbulletin...3354#post73354