We are still actively working on the spam issue.
This page is something I had seen before. OS X does meet the requirements for POSIX certification, so it is POSIX-compliant. Maybe not fully, I admit, but compliant nonetheless. Functions that are marked as optional are not required to be implemented. Code that needs to be portable cannot assume they will be present.
This is why build systems such as Autotools allow you to test whether certain functions are available before compiling code that uses them.