Why does enhancement necessarily require breaking changes in the APIs? Apple has a huge amount of experience in building C-level APIs that support far-reaching forward compatibility.
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.
Because the OpenSSL 0.9 APIs have some serious issues, and there are quirks in BIO destruction, etc, that couldn't be fixed without breaking a lot of code. That's why they maintain two trees; 0.9.8 for compatability, and encourage people to use the 1.0 tree, which not only has some new features, but also some important API fixes and improvements.
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.
