> This is a very old restriction based on the teletype console heritage.

   That explanation seeks to shift the blame to innocent hardware from a
very poor implementation decision which afflicts how many UNIX variants
other than HP-UX?  (Any?)  "@" and "#" may be "special" characters, but
they're certainly printable, and all the Teletype (tm) terminals I ever
used had a CTRL key which could be used to send _really_ special
characters.  My motto is "Change is bad", but I'd make an exception for
a change which would fix this particular out-of-the-box lameness in
HP-UX.

> [...] OpenVMS [...]

   VMS may have many flaws, but, so far as I know, its terminal driver
software does not ordinarily intercept any of the characters which are
legal in passwords.  Unlike one operating system which I could name.