Then that's too bad for anyone who tries to use non-standard shells. It's one thing to violate a vague, rarely used standard. It's quite another to violate what is most likely the most broadly supported standard on *nix systems.
Dash is Debian's default non-interactive shell, and it isn't POSIX compliant. The only way to get POSIX compliance on Debian is to switch to a different shell (e.g. bash).
