Actually that is NOT true. AP is completely based upon 485, it was seen as an interim measure given to people who wished to travel abroad while their AOS is being processed, hence the words "Advanced Parole". As soon as your 485 is adjudicated (one way or the other), all documents existing upon its validity, (EAD/AP), lose its validity! If you have been following the posts of people who have gone for stamping you will notice that they had to turn in ALL the paperwork, like EAD's/AP's etc.
Bottom line you CANNOT travel after AOS Approval on your AP! The only exception to this case is if you are approved, while outside the country. In which case, you are sent to defered inspection, for stamping, after entering on a valid AP.
The only legitimate way to travel after AOS approval is on the I551 stamp or the plastic card itself.