I should have been more precise: yes, they are introductory textbooks which accompany courses. I was defining academic as "it's a textbook of any level" not "it

I should have been more precise: yes, they are introductory textbooks which accompany courses. I was defining academic as "it's a textbook of any level" not "it's graduate level only". Leanpub has also been used to publish work based on dissertations (which is as academic as it gets), and those works obviously have far fewer sales.