How many "Cambridge"s in one line? (Citing a book from C.U.P.)
There's really no harm in adding clarifying information.  Obviously, we need a city name if we get "University of Georgia Press" because there are two very different University of Georgias in the world.  One located in Athens (Georgia, USA — not Greece!) and the other located in Tbilisi.

Likewise, if we see a publisher we're not familiar with, and the citation is only "Athens", it's nice to know at a quick glance whether we're talking about the American Georgian city, or the Greek one.  The topic of the paper make dictate which one is the "expected" one — if we're talking Atlanta politics, we can assume Georgia, unless otherwise specified, and if we're talking Plato, we can assume Greece.

Ultimately, though, it depends on the house style. If the house style includes the city, they'll do it for all publications, no matter how obvious one would think.  In your specific example, it's undoubtedly an overzealous copy-editor who is probably accustomed to having "Harvard University Press, Cambridge" and fixing it to "Cambridge, MA" to clarify.