My hunch is that most ac units aren't that sophisticated, and they just pump air that is "cold enough" or "hot enough" and pump it until temperature rises to the specified value. Is that right?
The Thermostat temperature is of the room, at the thermostat. The thermostat has a differential of about 1 or so degrees. Meaning if it is set for 70 deg, it will kick on @ 69 degs., then off @ 70 deg. The actual temperature of the ducts will be something different.
EDIT: The question is about AC so it is ductwork. Each register is likely to be at a somewhat different temperature & CFM due to duct length, size, how many turns, etc. This is often measured with an anemometer.