Is it necessary to write "United States of America" in bibliographies when describing the place of publication?
It's a good idea to take a step back here, and think about what the purpose of the bibliography is. Ultimately, it is supposed to allow a reader to unambiguously determine what publication is being cited, and further to help them get a copy of the publication.

In order to achieve this goal, I'd argue that specifying the location of a publisher is in most cases an anachronism. Given there is only a single 'Blackwell Companion to Phonology', which I can find in seconds with a web search, I don't really need to know that the publisher is located in New Jersey. We only still do it out of tradition. Incidentally, a far better way of unambiguously referencing a book is to state its ISBN.

However, bibliography styles may require that we include a location. In your case, you are unable to find a single 'correct' way of stating location for your bibliography style. So I would say, do whatever you want. Frankly, even if one of these is 'correct' under your bibliography style, I doubt anyone would notice, and if they did notice, I doubt that they would care. My personal preference would be towards brevity (e.g. Hoboken, NJ, USA).