I might have chosen different wording but the main reason I started with "IMO", is because it is not explicitly written.:)
Here is why I believe it has at least been decided for me.
The style guide says "use their conventions instead of ours." and "using the [location] names that people at the time used".
I have done a lot of research in Essex County, Massachusetts, and much of the State. The single convention that I observe being used is to only include what is necessary to avoid confusion. This is not the same as some official name, like "Town of Boxford".
There is an implied context already applied when location references are used. It's not true in all cases, but it seems that birth/death/marriage registers would use just the town name. For example, the Boxford register would have the bride born in Boxford, and the Groom born in Topsfield.
Another example was on some tax records was a notation, "Died young in Orleans".
Most earlier references I have seen, the "convention" only uses the city/town and State as "Rowley, Massachusetts" and later references "Rowley, Mass." I rarely saw or see source material that includes "USA", "United States" or "United States of America".
The problem with this is that those conventions used by the people at the time used, also knew what those conventions were.
There would not have been any confusion about the location "Rowley, Essex, Massachusetts, USA", so why would they want to use "Rowley, Essex County, Massachusetts, USA". when adding county would certainly have been redundant.
Two genealogists want something different and the guidelines should be used help resolve the issue, not let it linger. I believe the "Convention" does not include "county" and that the familysearch.org defaults to the Convention used at the time of the event.
This is just my Opinion.