Oil pressure is generated by the converter turning the oil pump, makes no difference what gear it's in. Park is no different to the trans than the car sitting still in neutral, same result, the output shaft doesn't turn.With the early FOMs having a propensity to break the case center web by putting them in reverse with idle speed high, I always thought Ford wanted to lessen the chance of that happening by starting in N. Still, most people would be backing out of the garage in the morning, so maybe that wasn't the issue.