Much like the other Beej guides, the target isn't that tightly constrained. This aims at POSIX options, and attempts to cover gotchas for cross-platform code.
Not to mention that just because you're only developing for Linux doesn't guarantee you'll have Binder or D-Bus.
Yes, which is why I highlighted that it is incomplete if you are not limiting yourself to just POSIX. It's important for readers to understand the scope of what is contained in the guide as it would be easy to think this is all the IPC mechanisms Linux offers.
>developing for Linux doesn't guarantee you'll have Binder or D-Bus
This is technically true, but everywhere Linux is used will likely already have one of them: embedded, mobile, desktop, server, etc. For D-Bus you can even have it work in a peer to peer mode where you don't need the daemon.
Neither are present in OpenWRT family, for instance.
OpenWRT has developed "ubus" as kind of a dbus-alternative, but it's definitely complicated to work with effectively.
Classic (Beej style) IPC though works fine.
Not to mention that just because you're only developing for Linux doesn't guarantee you'll have Binder or D-Bus.