I came to the same conclusion about using Amazon payments for everythingfunded.com (my crowdfunding site). After testing on the sandbox and moving to a production payment account, I got the same letter. "We are currently not on-boarding any new crowd funding/social fundraising sites at this time." So after some comparison I moved to Wepay. They can handle a 'marketplace' or three-party transaction and I liked that stunt with the block of ice.