psql \du and \dg commands.

Hello,
I don't really know since when those commands are provided by psql, but I
found them recently and was quite annoyed by the output given by both of
them.
Though I find that the \du command's output is quite accurate, I wonder why
\dg gives the same informations ?
I would have expected to see the group names in a left column, and the list of
users that belongs to this group.
I know I can get the information by fetching rows of pg_group system table,
but I was just wondering about this issue and see what you here would think
of it.
Thanks for any suggestions about this behavior.