If you want to receive the same result that you receive with the right outer join query you have to define the join between titles and sales (see below)...

select a.au_id, b.title,
c.qty
from titleauthor a,
titles b,
sales c
where
(a.title_id =* b.title_id)
and (a.title_id =* c.title_id)
and (b.title_id = c.title_id)
order by a.title_id

That said, definitely use the second query.