You have omitted the last part of the sentence from your quote about the 'Periodicals' guideline. It continues, "nor incompatible with this guideline". That is, the policy for the titles of books also applies to periodicals, and there are no special additional guidelines for the naming of articles about periodicals. Additionally, under the illustrated example of the Origin of Species, the guideline states, "If an authoritative edition of a book has letters of various size on its title page, everything after the largest print is (usually) considered "subtitle" in the context of this guideline".