Date or Documentation bug?

Good evening,
I am not shure if I discovered a Date or a Documentation bug....
The Manpage says if postgres is started with the option "-e" it
uses european date-style in the format "dd-mm-yyyy". But this only takes
effekt if I select datestyle=Postgres instead of the default "ISO".
With Datestyle=ISO it is always "yyyy-mm-dd", no matter if I choose US
or
European style.
With this behavior the postgres option "-e" does rather make any sense
to me.

Greetings,
   Holger
P.S.: Is there a way to change the Datestyle to Postgres without a
SQL-Statement,
e.g. ENV-Variable or config-file?