Why Won't Nintendo Accept American Express?

I wanted to purchase some Wii points on the shop channel only to find out that they did not accept American Express (My only card). I checked thier website and found no explination.

Suggestion:

American Express usually charges a business a higher % of a sale, so many businesses refuse to take it. It cuts down their profit margin.

Every time you buy something on a credit card the SELLER pays a % fee to the credit card processor. It varies for every business but American Express is almost always higher than Mastercard and Visa.