"""I don't know, maybe the author is trying to do something with the iPad which is simply not supposed to do. The iPad is beautiful, pleasant to use etc. but writing a book on the iPad is maybe not the things one does. I use my tablet to write — quite a lot — way slower than on my regular keyboard, but with time to think."""

You can pair the iPad with a bluetooth keyboard and write away at full speed.

And with something like LaTeX you won't even have formatting to slow you down.