Here's where its beyond dumb. We get charged to my gas by the BTU. If the gas is 10% N2 90% methane, I get charged 10% less than if it were pure methane, but the energy, work, is the same. Likewise, a gas mixture of methane and ethane is charged more than pure methane.
The system was set up because the regulators had the wool pulled over their eyes. The transmission companies made huge amounts of money for the first 5 years. Then as the rate baseing kicked in, they are not making any more money, but the guy shipping high BTU gas pays more than the guy shipping low BTU gas, it should be the other way around.