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.  <i>In the event we do this</i> 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."<p>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.<p>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 <i>much</i> 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."