I was thumbing through the new Grant and Sherman friendship book in the bookstore and noted the same strange source citation method I had seen in another recent Civil War book. The notes are not cited with numbers placed throughout the text, rather they are grouped at the end of the book by page number with the following method:
Page Number, "First two words of passage to be cited...last two words", Source.
55, "Lincoln said...a general.", O.R.
55, "Stanton raged...the rebels.", M.O.S.
and so forth.
I seem to recall that Goodwin's Team of Rivals uses the same method. I personally find it a clumsy methodology and unnecessarily burdensome to the deeper readers who wish to examine the notes. Clearly, it is an author/publisher compromise between the sales requirements of pop history and the author's desire for his or her work to be treated as serious history. I wasn't aware that this was even an acceptable method of citation (maybe some of our friends in the publishing arena can comment on this).
I remember reading an interview several years ago with an editor of a major publishing house. He stated that, all other things being the same, the mere presence of notes can take a book from successful sales numbers to an utter commercial failure. Those tiny superscripted numbers scattered throughout the text are oh so intimidating.