The only person who made a decent argument is Ekaton. I agree that troops sitting on the road should completely block supply, no matter what. I didn't go into specifics about this, because if you have troops sitting on your road, you are in way more trouble than allowing a trickle of supply through ZOC can help.
The fact that enemy ZOC hinders movement is an archaic limitation of the gameplay system, it does not actually reflect the reality of the war at all. A single, unsupplied unit, can zone your entire capital in a single turn; yet it exerts enough power and influence to increase your AP costs? That is unrealistic and completely broken.
I am not asking for ZOC to make sense.
I am asking for supplies to flow through, in a limited manner, through enemy ZOC, so that situations where a single rambo biker cuts off your entire front line supply is not such a binary thing, after he crosses mountains, millions of miles away from his nearest supply road. Naturally, if a powerful force does it, they will take much more than a single hex, or even three hexes, and cut off supplies; that is just an organic development that will happen.
The problem with becoming too specific about whether troops are sitting on roads or not is that it will make the logistics calculations take longer than they already do. Even letting supplies through ZOC will likely significantly increase the computation times. But I'd rather wait longer than have to marvel how a bandit can cross my road, bugger off into the mountains, and my mindless, unintelligent truck drivers go 'Nah boss, can't do, it's not our ZOC, but I'll go down this side road that leads to nothing'.
Consider also the fact that enemy units do not play by the same rules. Empirical evidence suggests they do not pay AP for terrain penalties or your ZoC, so they can gobble up with impunity. Especially minors, who don't need supply. In that case, ZoC binarily blocking supply is just a punishment and a weird quirk that you have to deal with it in a nonsensical manner, like traffic lights and LIS side roads. But unlike traffic lights, holding back militia or troops -never- works. If the AI is dead set on crossing your road, it will do it somewhere. It will walk right past your militia and cross the road, and then run off.