The semi-official reason though is that OpenSSL doesn’t offer API compatibility between versions.
http://opensource.apple.com/source/Security/Security-55471/l...
You are aware that GnuTLS had a very similar "goto" style verification bypass bug, and that OpenSSL has had several flaws and broken stuff discovered, including the major recent "Heartbleed Bug".
The semi-official reason though is that OpenSSL doesn’t offer API compatibility between versions.