Security...

[greep%su-dsn at sri-unix.UUCP]

Unix has that too.  You just look at the password file for someone with the
same encrypted password as you, and it's likely that the plaintext is also
the same.  This scheme can also have its advantages; if I want to set up a
login for someone remote, who doesn't want to have to send me his initial
password in a message or have the account set up with no password, he can
send me the encrypted version and I can just install it that way without
knowing the plaintext at all.