The perfection should be downstream of the project's coded standards, not downstream of the faithful implementation of the designer's work. Some designers are really good about maintaining standards-- but the book would argue all that effort should be spent elsewhere.

It's basically "the arbitrary padding the designer liked in the moment" vs. "the standard padding that's everywhere in the project." This book argues you should always use the standard padding. Your product should be pixel-perfect, just not in the PSD-to-HTML sense.