I think it's because the author thinks "via" text is a negative thing?
They run an email forwarding service, so their SPF records will fail, but an untampered email should still pass DKIM. in fact, that's how most email forwarding setups work. If the message is tampared, and re-signed with the forwarding service's DKIM key, it's correct for Gmail/email-client to show the via-text.
