I don't think it is fair to brush it off under "same bucket; doesn't count." The syscalls are still different and there's quite a bit of nuance. I mean the lines you're drawing are out of superficial convenience and quite arbitrary. In fact, I'd argue macOS/Darwin/XNU are really Mach at their core (virtual memory subsystem, process management and IPC) and BSD syscalls are simply an emulated service on Mach, which is quite different from traditional UNIX. The fact that as a user you think of macOS much more similar to Linux is not really reflective of what happens under the hood. Likewise NT has very little to do with Win32 API in its fundamentals but Win2k feels the same to the user as WinME, but under your framing, you'd same-bucket those.