I do have a theory that the port may remain on the Sport models because I suspect the "movement" on the Sport is installed in the case permanently with adhesive. As such, it stands to reason Apple might maintain a diagnostics capability to troubleshoot issues at the Apple Store before simply trashing the defective unit and handing the customer a new one. With the Watch and Edition lines, it would make more sense to simply pull the movement out and replace it - Atomic Delights
Interesting article on the production process of the Apple Watch. But this paragraph ran specifically true to me.