Although I refrained from making this comparison in the book, since it would have been complicated to outine and defend and I don't really know about much literature on the subject, the obvious comparison is to marriage, which the state - for good, I think - encourages and incentivizes. Perhaps, just like there is a cultural supposition of monogamy and some sort of civil union for many people (with exceptions, obviously), there should be the same supposition for the provider-patient relationship.
What kinds of incentives are in place for civil unions or marriage? Plenty, ranging from the financial (tax credits) to the sociological (name changes, fancy parties) to the recognition in various contexts, including health-care related, that the partner/spouse has a special place in the hierarchy of information sharing or decision making.
The same could, or should, be said of the place of the PCP in the health care relationship. There should be incentives for patients and providers to maintain that relationship; requirements that specialists communicate, and run major decisions by, the PCP-patient dyad, and perhaps even social recognition (parties? name changes? maybe not - but something ceremonial) when that relationship is cemented.
There is something else that happens in relationships: mistakes can be made, and, providing they are not so serious, negligent, or ill-intentioned as to be inexcusable, the relationship survives. There is plenty written about the best way to come clean, ask for forgiveness, and correct the processes that led to a mistake, whether in a relationship between two adults or in the setting of health care. Just as a relationship - in the best of cases - provides a cushion for a mistake, the special connection between the PCP and patient can sometimes withstand serious error.