The manual is out of date.
This was modified in one of the betas and made permanent in the last official patch.
Can't remember the exact criteria, but it HAS changed.
Perusing the change log for the betas in michaelms thread can document this.
This is probably in the top-5 most asked questions. The manual IS long out of date. The change was made in an early official patch.
The patch notes themselves have a typo, which I've corrected.
"48. Gameplay Change: Allow ship withdrawals at any on map level-9 port and some smaller ports with no enemy nearby. Ships can always be withdrawn from any off- map port or from any TF that is currently off map. Ships that are not badly damaged can be withdrawn from some on-map ports or from TFs in certain on-map regions. For on map, ship may not be on fire, total damage may not exceed 99 and no individual damage type (system, floatation, engine) may exceed 50. Ships may not be withdrawn from any on-map location where the enemy has air superiority. The intent is to prevent withdrawal as a method of saving a ship that stands a good chance of being lost or further damaged. On map withdrawal ports are set based on the historical exit locations for ships leaving the Pacific:
1. Any level 9 port.
2. National home ports of the United States, Canada, India, Australia, and New
Zealand (with no port level requirement)
3. Any level 7 or larger port on the US or Canadian West Coast.
4. Any level 7 or larger Indian port West of Ceylon (including Ceylon itself)
5. Any level 7 or larger port in South Eastern Australia, plus Perth.
6. Any level 7 or larger port in New Zealand."
Change is to swap "West" for "East" re Ceylon.