This has bugged me for quite a while, a few days ago enough so that I actually grabbed the strace source code with the intent of compiling it on OSX, at which p

This has bugged me for quite a while, a few days ago enough so that I actually grabbed the strace source code with the intent of compiling it on OSX, at which point I discovered the real reason: ptrace on OSX doesn't support the PTRACE_SYSCALL flag. (I gave up at that point.)