To prove the point reductio ad absurdum, I took the entire Japanese navy out to sea in the '41 scenario after taking all of the DEI turn 1. The total upkeep is under the oil production. This makes the game unplayable in 1.00, as the only leash for Japanese aggression (not to mention historicity) is oil...
Edit: Instead of screenshotting every single fleet I ran the turn a few times until everything was out of supply to demonstrate that they're not in port. Upkeep remained the same over the 3 turns.

