If you pay for the service after consuming it, you are by definition using a line of credit. For cable you'd have to load a prepaid balance into your account,

If you pay for the service after consuming it, you are by definition using a line of credit. For cable you'd have to load a prepaid balance into your account, from which the the cable provider could debit by usage. As soon as the balance hits 0, service is shut down. Most people don't want to deal with that hassle.