They only deliver to houses (I wish I knew why they don't want to deliver to a post office box)

Because post office boxes can't sign for proof of delivery.
Ever since Australia Post brought in this E-Post thingie, ALL parcels have to be signed for, not just Registered Post. That's why I have all my parcels delivered to work, because if there's nobody there to sign for it, then they just leave a little card in your post-box and you have to go and pick up the parcel yourself. Australia Post: we DON'T deliver.

(I do get rather ranty about this, don't I?)