Huh, you're correct. I had this memory of having funded someone via Paypal, even could visualize the Paypal email confirmation, and I go and look, and it is indeed an Amazon Payments confirmation instead. Weird lapse of memory; sorry for the noise!
(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.)
https://cms.paypal.com/cms_content/US/en_US/files/developer/...