That's some kind of logic.
I'll put it this way, it may not be a "must" win situation, but it certainly puts more leverage on the rest of the games this season when they aren't playing a team in their division that is directly in front of them. Maybe not a must-win from the academic definition, but very important still.
By your reckoning, the only must-win game is the one that eliminates them from the postseason. Make's sense.