Well, strictly speaking, you do not normally need a passport as French national to visit the DOM/TOM, unless you transit via a third country (an ID card is enough) but, yes, there is no automatic equivalent between entering a separate state and being subject to administrative formalities on entry, both in the sense that some states allow free movement of citizens between themselves even without international travel documents (such as the 'common travel area' between the UK, Ireland and UK Crown Dependencies) and, conversely, some states can decide to restrict access to certain parts of their territory even to their own citizens subject to the possession of specific or generic travel documents.

When you add to that the difficulties resulting from territories with complex, ambiguous or disputed legal status, it becomes even more obvious that treating the requirement of a passport on entry as a reliable indicator of the crossing of a universally recognised international border is problematic.