> Is it more or less surprising for `rm -rf /` to be special?

A few years the POSIX folks declared that the behaviour of `rm -rf /` nuking the entire file system is a bug.

IIRC, one of the Sun Solaris folks (Cantrill? Gregg? Other?) thought the behaviour was dumb and argued successfully that it should not be work that way. Any implementation that does it is not POSIX-compliant.