Now, if the line from the CO (where the DSL terminates) to the internet was a significant bit of the cost, I'd agree with you. But my understanding is that the line from the CO to the 'net is a very small cost compared to the cost of all those copper pairs.

You also have a point when it comes to shared-loop technologies like cable. Metering is probably the most fair way to decide who gets what percentage of the limited fixed loop. (and probably the best way to get the telco to add more capacity when a loop becomes overloaded)

I'm just saying, the last-mile has many situations where running the connection, regardless of how much you use that connection, dominates the cost. And in those cases, "unlimited" (up to your port speed) billing makes a whole lot of sense.