I was most surprised that they don't include disclosure of this relationship when mentioning Amazon in the article. I thought that was comme-il-faut of serious journalism.
They should have a disclaimer, but it's not exactly an ad for shoes at Zappos. As a customer I'd be worried by the instability such a big unproven change could bring to deliveries and customer support. It's a pretty fair and interesting article, but that's just my take.
(Jeff Bezos, CEO of Amazon, parent company of Zappos, owns the Washington Post.)