{ 1 } - holds in all cases in an exceptionless manner.
{ 2 } - is subject to various implicit qualifications.

The duty needs to be qualified since, for example, we might be psychologically unable to be consistent at a given moment. Since "ought" implies "can," we can't then have a duty to be consistent.

Also, the consistency duty can be overridden by other factors. Maybe Dr. Evil will destroy the world unless we're inconsistent in a small matter.

All our consistency duties (even the golden rule) are subject to the same implicit qualifier. Section 2.3 of the book formulates this more carefully and compares it to a qualifier needed for logical principles.