There are some critical ways of creating emotion in games that aren't discussed in this book, such as music, art, animation, and level design. All of these important and immense subjects deserve books in their own right (and many such books already exist). The line had to be drawn somewhere; a subject needs to have a border or an edge.
Even if you work in these other areas of game creation, you may very well find tools in this book that are applicable to your own art. Sparks have a way of spreading.