I'm struggling to understand your criticism. Why the authors decided to put 12 instead of 24 or 100 (or whatever) is irrelevant. What's relevant is whether the

I'm struggling to understand your criticism. Why the authors decided to put 12 instead of 24 or 100 (or whatever) is irrelevant. What's relevant is whether the factors themselves are meaningful. The common thread is covered in the introduction. It's about building services that back web applications in a way that makes it easy to deploy and manage them.