Prepaid credit cards are a very valuable tool for anyone using the AWS free tier of service. Its an extra layer of protection if you ever do get DDoS'd.
No, I don't care if it means amazon doesn't get paid for the bandwidth consumed by an attack. Sometimes all I care about is not getting a 10k or bigger bill at the end of the month for what was advertised as free. IMO they really need a way of automatically shutting down VMs that go over limit instead of just charging the credit card on file.