With a broadcast network, the same signal is piped past every user, regardless of whether that user is actually using the service. You can turn your TV on and off until your fingers bleed without gaining the attention of a single executive at your service provider. The same is simply not true for Internet access. If you are using the network, someone else is not. If we all use our Internet service an hour more next month, the ISP will have to install more modems per customer.
Variable costs demand variable rates.
Remember, you do pay a variable rate for gas and electricity. The problem is that people keep pushing the envelope in terms of Internet applications. Moreover, innovation of arbitrage software is likely to continue for some time. The subtle difference here is that a microprocessor in a PC is restricted to use by one individual. You can then communicate with yourself at unbelievable speeds.