I'm not sure this is the case here, but it might be the difference between the actual text itself and the representation, arrangement, and style of the text as exhibited in the book. This happens in music, where a given Mozart concerto, for example, is in the public domain, but that doesn't mean you can photocopy a given sheet music of the concerto and hand it out; the notes themselves are in the public domain, but the particular typesetting of the specific document is not.
This was an issue recently with the Google Book Search deal. Even though the books were out of copyright or orphaned, Google owned the copyright to the scans, and would only give a non-transferable license back to the universities.
Google does have a copyright on the collection as a whole, even as they do not gain any extra rights on the underlying public domain material. It's sort of weird, but it does make sense.
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I'm not sure this is the case here, but it might be the difference between the actual text itself and the representation, arrangement, and style of the text as exhibited in the book. This happens in music, where a given Mozart concerto, for example, is in the public domain, but that doesn't mean you can photocopy a given sheet music of the concerto and hand it out; the notes themselves are in the public domain, but the particular typesetting of the specific document is not.
This was an issue recently with the Google Book Search deal. Even though the books were out of copyright or orphaned, Google owned the copyright to the scans, and would only give a non-transferable license back to the universities.
Scanning a public domain work doesn't give you copyright over it. See Bridgeman Art Library v. Corel Corp.
"...which ruled that exact photographic copies of public domain images could not be protected by copyright because the copies lack originality." http://en.wikipedia.org/wiki/Bridgeman_Art_Library_v._Corel_....
Google was probably giving a limited license on the collection copyright, which is much less protective than "normal" copyright.
It's harder to google for that term than many other copyright terms, but here it is from the horse's mouth: http://www.sacred-texts.com/sect103.htm
Google does have a copyright on the collection as a whole, even as they do not gain any extra rights on the underlying public domain material. It's sort of weird, but it does make sense.