I don't think the "arbitrary" is justified. It's a group of people who use a platform over which a reasonable amount control over typography and layout can be m

I don't think the "arbitrary" is justified. It's a group of people who use a platform over which a reasonable amount control over typography and layout can be maintained. That's not arbitrary if your goal is to create books that conform to a particular standard. (it's also possible there are technical reasons. The book is written in Pollen, Butterick's publishing system for web-based books. I don't believe it supports output to other formats.)