Moorcombe's field guide includes these outlying islands which, despite
political maps, are certainly part of the Australian zoogeographic map.
Unless I'm mistaken, so does Pizzey's. It would make a somewhat weighty
tome, and for this reason alone I understand their exclusion, but for many
reasons, New Guinea's birds could be included too. Of course, field guides
are somewhat designed to suit the needs of the market and so, just like
street directories, are sold in chunks which relate to their most likely
use. This makes sense to me and if I wish to know about birds in other
localities, I buy the local guide.
Regards - Ricki