PW,
I belive they use the fenced in area much like a Johnny House is used for quail.They are allowed to free roam during the day, assimilating into the surrounding habitat, then are called back into the safety of the fenced area to feed and roost. Eventually they spend more and more time outside the fenced area until they don't come back at all, or are into the hunting season.
We know of a farmer in Bradford County Pa. that has been doing something similar with some very good results!
The Pennsylvania Game Commission raises it's bird in a more traditional way, although I must say they are very healthy birds. Yes, they go from the flight pen to the field.