I think that Kickstarter has their shit together, and the risk of a chargeback from Kickstarter to [project leader] is relatively low, compared to the risk of a project funded directly through Amazon Payments.
I don't know how indiegogo works, but in the case of Kickstarter, I would assume that Kickstarter is collecting the payments, arbiter of refunds in the case a goal is not met, and does not have access to the money in the interim.
Then Kickstarter uses Amazon Payments to disburse the funds to project lead? I am uneducated and did not contribute to the fund, so I don't really know how it works. Can you enlighten?