I think this is part of the overhead costs others point out in this thread. Why Manhattan? It looks more and more unnecessary as the years pass. Sourcebooks is based in a suburb of Chicago. Harlequin is in Toronto. Artists and editors can live anywhere.
Overhead is a cost of doing business; it applies to things like space and electricity and software and hardware, and support staff.
An awful lot of the people who do the actual hands-on-work of publishing aren't in Manhattan, but the accounting and executive folk still are, especially for the very large publishers. For instance, Macmillan and their parent company have offices in the Flatiron building, but increasingly editors are all over--and paid on 1099s.
It's not broken out specifically on P & Ls. Quite often the book uses out of house staff for design, or editorial, so those costs will be listed on a P & L.
But other than the printing and binding costs, I don't see why acquisition, editing, art, proofing etc. aren't considered shared for day-and-date release.
Once the file forks, going to printers or to ebook production staff, the costs differ, but up to that point it is the same file, the same product and shared costs.
Actually, I think looking a P and Ls makes some sense.
Some samples (these are from a variety of publishers, of various kinds):
http://pimpmynovel.blogspot.com/2009/10/p-1-of-4-basics.html
http://gropenassoc.com/blog/2009/11/a-typical-trade-titles-pl/
http://www.stevenpressfield.com/2011/09/a-matter-of-infinite-hope/
http://www.annagenoese.com/article_series/demyst/free_articles/article_p_and_l.html
These days the P and L master spreadsheet is often a closely held trade secret document, but I've seen long-term professionals do a P & L on a napkin.
Note that during the course of a book's lifetime—from proposal before acquisition to release and tracking—the P and L is a living document.
This article has a breakdown as well.
There's potential for some quibbling from some publishers, but it does seem fairly accurate based on my experience in commercial print and epublishing.
Based on everything I know, and I've worked on a lot of books, print and digital in production (not to mention as an author and editor), that 10% of cover price as a fairly reasonable ballpark figure for the difference in production costs for an ebook and a printed book of the same text is pretty accurate.
Keep in mind that the assumption that a publisher will have to keep stock in warehouses is not so much the case these days. Publishers still do this for textbooks, but back in the 1990s Random House had a warehouse just for the Modern Library. Now, they instead do smaller print runs just in time--in part because of much better inventory and shipping data.
You will see a more noticeable disparity between production costs for a printed book with lots of color images and an ebook, but for text-dominant books, not so much.