I read an article once on Disney heroes that was talking largely about the fairy tale convention of absent or ineffectional parents, particularly mothers.

That's how SPN reads to me.

Mother is dead and acts only as a motivating force for revenge, Father is absent, to free up children to go have adventures. It's pretty standard mythology stuff.

How much more deeply do we need to read it? This is STOCK plot stuff from forever.

YMMV, of course.