From the introduction:
Creating a Role Playing Game is hard.
That’s not a complaint -- we like the
challenge -- but just a comment on
the fact that when creating There’s a
Game in this Book there were many ideas we had
to leave on the cutting room floor for sake of page
count. While some RPG books can get away with
thousands of pages of content (which is often
times repetitive and almost always tedious),
we’ve tried to keep our books svelte and fun to
read -- a one thousand page tome just isn’t our
speed.
While writing the zombie entry in the main book,
for example, there were a host of specialized
zombie ideas we wanted to include but just didn’t
have the room. As a compromise, we selected
the best ones from the list of everything, the ones
we felt had to be there or people would be left
wanting, but we knew we were going to revisit
zombies in an expansion. This expansion.