I also wondered about the "Play" rename. I assumed it happened because they have such a strong priority coming from above on movies/music this became the central thinking. And apps/books became less relevant.
I don't think Play was meant to exclude apps so much as recognize that the apps that sell the most tend to be games (or at least it looked that way the last time I compared the iOS and Android leader-boards).
Books, on the other hand... it's clear no one was thinking about them (but that's par for the course, I'd say).
