I don't know much about OS X except that they use the Mach-O executable format (unlike PE in the article), but I know that the ELF format as used on Linux and many other unixes is similar in that it also has a section where the code resides, so they can encrypt only that part. And inserting checks into the code is also portable of course.

It would have been interesting if they had talked about different platforms, but alas, it's quite a superficial article...