I'm not sure what you're saying here.

Obviously, ISPs could charge by the byte. To my knowledge none do, for reasons others have mentioned already. We don't like thinking about the marginal cost of web pages, and nobody wants a nasty surprise on their internet bill at the end of the month.

Tiered pricing isn't germane to metering. A power company might place me in one service tier, and a megawatt aluminum smelting operation in another. They might pay less per kWh than I do, but we both pay ~20% more if we use 20% more power. OTOH, while Time Warner will let me pay an extra $10 to upgrade from "5Mb" service to "15Mb" service, my monthly bill is fixed regardless of my usage level.

Unless you count trash pick up as a utility. Would that it were tiered/pay per lb... would encourage less waste.