well, there *is* already airflow over the elevator as soon as your speed is above zero, whether useful or not is depending on the situation. From experience on traditional and Airbus aircraft I can tell that there is already significantly more pressure on the nose wheel after a few meters during TO.
Airbus could have written "push the stick half full forward at 20kts", but that also makes not much sense, so it's better to start with the stick position at the start of the TO procedure.
Above 80kts the pressure on the nose wheel is so strong that it is a good idea to release the stick. I'm pretty happy that AI had the cleverness to write this down, because I see so many people pushing that yoke so hard (on other types), I sometimes fear that there will be a hole left on the runway...
HB