Costco blew it. Their policy might be 14% markup only, but you can bet your ass that if they wanted to continue the relationship with Apple, they could have made an allowance.
Look at it from another view. Apple needed Costco far, far less than Costco needs Apple. While I am not privy to how many devices Costco sold that had the Apple logo on it...to simply banish them from their premises due to a pricing issue with Apple is shortsighted on their part. Every device that could have been potentially sold in a Costco store...is now gone, seemingly forever. Apple didn't lose any, because other retailers exist to sell their product.
Lastly, I am not familiar with Costco. Yes, I'm aware of what they are, but the nearest is 400 miles from me.
Costco needs Apple? Why in the world would you come to that conclusion? The amount of Apple products sold by Costo must be a tiny, tiny fraction of their business. They won't miss a beat by not having Apple products.