Cameron,
I agree with your "I don't see the need..." statement, and yet this is what the specification says (from p. 9.1.24):
The default schema-level mapping for unidirectional one-to-many relationships uses a join
table, as described in Section 2.1.8.5. Unidirectional one-to-many relationships may be implemented
using one-to-many foreign key mappings, however, such support is not required in this
release. Applications that want to use a foreign key mapping strategy for one-to-many relationships
should make these relationships bidirectional to ensure portability.