Thank you everyone for your help. My wife had me speak to the rep, who gave me 25k points to keep the card open. I figured it's worth it, as I wasn't going to get back the full $450 anyway. Now I have to decide what to do about cancelling the card in a few months.
My wife was just approved for an Amex Starwood Card. Will Amex now allow her to cancel the platinum card, and pro-rate the annual fee, based on her ownership of another Amex card, or does she need to own a charge card like the Zync?