plant upgrade costs, backbone upgrade costs, etc do no have anything to do with how much usage goes through them. you can pay for all of that with the monthly fees. If they really want to make this reasonable they will stop jacking the monthly access fees up every 6 months. Heck, maybe even lower it every so often.
So, because upgrades are a step function you can't smooth out the steps and charge people for their contribution to the need to upgrade? Because while one user at 300GB isn't a big deal on a DOCSIS 3 system, one hundred users at 300GB, plus other people on the node, would probably merit turning on some more DOCSIS QAMs, making a node split, or increasing backhaul...