endash not a graphic character?

I was surprised to find endash and emdash were not graphic characters in
en_US. I'm not sure if this is correct behavior, a bug in postgres or a
bug in my OS' collation definitions?

For example:

Dash:
area=> select '-' ~ '[[:graph:]]' collate "en_US";
?column?
----------
t
(1 row)

Endash:
area=> select '–' ~ '[[:graph:]]' collate "en_US";
?column?
----------
f
(1 row)

Emdash:
area=> select '—' ~ '[[:graph:]]' collate "en_US";
?column?
----------
f
(1 row)