On: GNU /bin/ed 1.6 released

"GNU ed is an 8-bit clean, more or less POSIX-compliant implementation of the standard Unix line editor."

If the main implementation of ed isn't even POSIX compliant these days, I'd say POSIX is officially pointless.

GNU has a long history of ignoring POSIX where they disagree with it. There's a much better chance that the BSD implementation will be fully compliant.

Not entirely - it gives people a way to say "Unix-clone" without getting sued.