While I voted "all of the above" I usually like MA books that are light on technique structure, and discuss more of the principles and theory. The history/legend is good, but ideally a good book should draw the line between the two (a style's verifiable history, and the legends surrounding it.)
The techniques and apps aren't bad, and can help enrich a book; but ultimately, books are better at communicating tangible aspects of the art it is about. I am somewhat biased, as I've never been able to learn from book images- at least not enough to REALLY understand the technique.
My two favorite books are "The Sword Polisher's Record" by Adam Hsu, and "Chinese Martial Arts Training Manuals" by Brian Kennedy and Elizabeth Guo. Technique is almost absent from them, but they are rich in all the other aspects. Despite the lack of technique though, Adam Hsu's book helped me to understand "Silk Reeling" better than any other media available.
"Prepare your mind..." "For a mind explosion!"
-The Human Giant, Illusionators