Please excuse me if this is a newbie comment, but I ordered two Marriott certificates with my MR points. When the order page showed no progresss in fulfilling the order even a week after I placed the order. So when I called, it turns out that Amex buys gift cards/certificates directly from Amex which fulfills the order and this can take up to 10 business days. In all fairness, I probably checked off some box acknowledging this but it's an anomily for MR where most orders come within a few business days. So make sure you order two weeks in advance for Marriott gift cards/certificates or prepare to be potentially disappointed!

On a related note, it appears that Marriott while restricted in what it can do with American Express by their agreement with Chase still has signifcant deals with Amex. Amex on their parts seems to buy Marriott gift cards and stay certificates directly. Marriott meanwhile offers Amex business charge card holders discounts through the Amex OPEN program as well as periodic offers to American Express cardholders.