The short version is "Take our EPUB file and upload it to the iBookstore".
We generate PDF, EPUB and MOBI. The #1 goal for us with EPUB
generation is to ensure our EPUB files work on iPhone and iPad (either in the Leanpub app or in iBooks). The #2 goal is to ensure they can be sold by authors in the iBookstore with no issues.
We are developers and do not believe in lock-in. We want you to use Leanpub because we are the best. We charge money and have a 45-day refund period because we are confident our service is worth it.