From my experience, DHL is a middle-man from the manufacturer's (or apple's, depending on how they set their supply chain up for this) warehouse to a USPS distribution center. Mine was shipped on a (short) DHL journey, and arrived via regular USPS priority mail.
Originally Posted by tibbar
From the looks of it, Apple is shipping out 3rd party cases as they become available in batches, instead of just shipping them individually as they receive them. (so if they get a shipment of several hundred of one case, they'll ship out all of them to their destinations at the same time, and then wait for the next full batch for more)