Budget News: Costco and Amex end relationship

For years, Costco has exclusively accepted American Express credit cards.  Well, as of March 2016 that will no longer be the case.  Amex and Costco were unable to reach a deal regarding their exclusivity agreement.  Therefore, come next March, Costco will no longer accept Amex card but instead will begin to accept Visa credit cards.  I can't see how this is not a blow for Amex.  I don't think people will stop shopping at Costco because they can't use their Amex card. However, I think there are many people who only have an Amex card because of the relationship with Costco.  Costco Amex cards account for 10% of all Amex cards.