Let me say that again: You don't buy ebooks. You license them.
You don't buy ejournals, you license them. In most cases, you stop paying, you no longer have access. Ebook collections in the library? In most cases, you stop paying, you no longer have access.
Unfortunately, David Dobbs just learned this the hard way. iBooks you licensed disappear if your phone has been unlocked or jailbroken and you do the update. You broke some aspect of the license so they stop their part of the license - providing the content.
Remember when Amazon pulled back copies of Orwell books from Kindles? It didn't matter if you held up your part of the license in that case, they found that a third party had broken the law.
Libraries are trying to write licenses to have "perpetual" access but in many cases this only applies if you license individual books, not collections. We also like schemes that provide a backup like LOCKSS, CLOCKSS, or Portico. AND we do everything we can to make sure we hold up our end of the license (no bulk downloading, only the people who are supposed to have access do, etc.). This is why we sometimes seem like the watchdogs for the publishers.
Just get your stuff from a library, then when it goes poof you can just check it out again. Or if not, maybe a third party (like B&N or Amazon) would prevent the iBook issue (if not the other issues).