> You'll find that, often, if not always, if you buy directly from a publisher, the ebook will be free with the paperback purchase. (Manning is one example, not sure about others off hand.)

Extrapolating “often, if not always” from one niche publisher is quite a stretch.

Random House, for example, does not do this.

https://www.penguinrandomhouse.com/books/713318/wonka-by-roa...

Neither does Simon & Schuster.

https://www.simonandschuster.com/books/Icebreaker/Hannah-Gra...