That's a major version change. You expect API compatibility typically with patch-level and minor releases.
Open source libraries like OpenSSL tend not to bother, because their model is that you recompile stuff whenever they make binary breaking changes. And there's nothing wrong with that, it's just not how Apple operates. But it's not something inherent in the concept of libraries.
It's important to note that you can in fact have both openssl library branches on your system and that isn't a problem. It's a mis-statement to refer to these things as breaking changes, as your 0.9.8 linked code is not going to break anytime soon.
iOS major version bumps frequently though...
Besides, Apple's major OS releases are executed like a major version number bump regardless of how others outside the company do things. These bumps include deprecation markers and warnings for APIs with planned retirement. There's no technical reason to remove deprecated APIs (keeping them around forever) to support older apps.