I'm not so sure that editorial would be right - just calling it editorial doesn't necessarily make all photos editorial. Some could easily be construed otherwise. There appears to be some value in calling it all art, but from what I have read this doesn't necessarily cover us either.
The idea of some wording is a great idea, particularly stating that the book is not for profit, which may make some/many lawyers realize it's not worth a fight because they won't get anything. This isn't total, I would think, since they could still sue and get someone's house. 
Since we are publishing this book, the laws are a little different from what I've read. One piece I read stated that people don't sue photographers, they sue publishers. So it's in the publisher's best interests to ensure that they obtain copies of releases for any photo which might require one.
Here's a few sites I found that seemed worth reading - though most have to do with photographing, and not publishing a book of photos.
http://www.publaw.com/photo.html
http://www.danheller.com/model-release.html
http://www.photosecrets.com/links.law.html
http://www.photosecrets.com/tips.law.html
One of my concerns has to do with property releases. From the last web site I found this paragraph quite important:
Only buildings created after December 1, 1990 are protected by copyright. Fortunately for photographers, the copyright in an architectural work does not include the right to prevent others from making and distributing photos of the constructed building, if the building is located in a public place or is visible from a public place. So you don't need permission to stand on a public street and photograph a public building. You don't need permission to photograph a public building from inside the building (although you may need permission to photograph separately-owned decorative objects in the building, such as a statue). You don't need permission to stand on a public street and photograph a private building such as a church or a house.
I've also heard rumors about some "public" places requiring permission. Trafalgar Square or Piccadilly Circus or something like one of those two.
So far, everything I've read tells me to play it very very safe, and not publish any photo which might require a release of any kind, unless a copy of such a release is obtained from the photographer.
I would love to hear differently, but I think I would have to pay a lawyer before i would think differently.