I agree with you. I really see no differences between 1 cell and two cells.
The basic difference between using the battery FET and not is the isolation. If the battery FET is not used and the battery is fully discharged, the current going to the battery/system will be the precharge current which may not be enought to power the system and recover the battery. With the battery FET the system can get all the power from the source. Battery detection is also an issue for the system if connected directly to the battery. The system most likely would not run during the discharge portion of the battery detection.