So sorry for the delay in responding to your question. I think this one must have slipped through the cracks.
Rule II.10.b refers to book titles, publications, ships, and pictures that would require some sort of emphasis in print.
For example, in a printed document, book titles are always in italics, underlined, etc., thus each separate title needs to emphasized individually.
Section 15.1d refers to names of birds. This would not require special print emphasis just because they are birds, so the list can treated as a group and double emphasis is used.
I hope this helps,