And here's the answer, from the author himself!
The books are each quite different and cover different subjects. Chronicle 1 is all about concept art, as you have seen, whereas Chronicle 2 picks up where that leaves off and covers the processes of turning concepts into a reality for the screen, so it is about make-up processes, making and animating digital creatures, talking with cast members about their roles, movement coaching, the scale issue, dialect coaching etc. Where Chronicle 1 is sketches and paintings, Chronicle 2 is photographic, with behind the scenes imagery and film stills. They two will be quite distinct and tell very different stories.
Other books in the series should cover other aspects of the films' production, with as little overlap or duplication as possible, and it is our aspiration that when viewed as a collection they can be considered comprehensive and definitive.
We're doing so many because we feel the subject matter demands and sustains it. It would be very difficult to cover the movies with any more brevity and still hope to be comprehensive.
Timing also plays a part. It would not have been possible to produce a book about the final digital creatures any sooner that Chronicle 2 (which went to print last week), because they weren't ready early enough. As I am sure you can imagine, Weta Digital were finishing shots right up till the final days before the premiere. Chronicle 1 was finished in August. On that note, as you may have seen, there are a handful of subjects not covered by the book. In each case these were things that had either not been designed when the book went to print or were intentional omissions on our part, held back to be covered more fully in a later book. Once the collection is done, everything should have hopefully found its place, but that story, just like the films, will take years to unfold.
We hope you enjoy coming on the journey with us.
So the first book will be The art of The Hobbit, and the second like 'The making of the movie'.
These really will be definitive!