PayPal's blog:

PayPal has permanently restricted the account used by WikiLeaks due to a violation of the PayPal Acceptable Use Policy, which states that our payment service cannot be used for any activities that encourage, promote, facilitate or instruct others to engage in illegal activity. We've notified the account holder of this action.

The rationale seems more convincing (at least from PayPal's perspective) than Amazon's wheedling about rights and redaction. But the timing, at 11:29 p.m. EST on Friday evening, suggests they do know the decision is something to be buried, not boasted of.

Update: In a tweet, Wikileaks says it was the result of government pressure.