Apple's mind-bogglingly greedy and evil license agreement
This seems to be a misreading.  My read is "If you sell the output of this, you grant us exclusivity.  If you breach exclusivity, we have a variety of options in dealing with you, including refusing to carry your work on our platform.  In the event we do this we don't owe you anything even if you think it sure would have been a swell thing if we had distributed through our platform and are inclined to sue us over the imputed lost revenue."Exclusivity is still a very cruddy contractual term for authors, if viewed against the universe of "all possible contractual arrangements", but it is far from uncommon in the publishing world.  I mean, everyone is pretty much in the business of exclusive distribution towards channels they control.  If you sign with a dead-tree publisher, they're going to want exclusive rights to be your only dead-tree publisher in a geographic, cultural, or linguistic territory, even if you could get someone else to kill trees on your behalf and double your sales that way.You'd have to weigh access to the Apple megaphone versus the sales you could be making through other platforms/channels.  If I were (hypothetically) going to get into ebook publishing, I'd take note that Amazon is much more generous (off the top of my head standard Kindle publishing requires no exclusivity and one of their programs wants just a 90 day exclusivity window for e-publishing).  This would allow you to simultaneously sell through e.g. your own site to a pre-existing fanbase and avoid the 30% (or whatever) rake, or do things like "Hiya I'm the author of five novels and counting in this sci-fi universe I created.  The first one is $0.99 on Amazon or totally free if you sign up for my email list."