In fact, it is specifically due to Amazon Payments simple mechanism for getting a pre-authorized token that can later be captured that allows Kickstarter to run that business

(PayPal now supports this through PayPal X, but did not at the time that Kickstarter was being first released. Getting access to this API from PayPal requires more authorization than from Amazon, but the result is also more powerful: you can hold tokens with no expiration and seemingly no cap.)