For the last 18 years, Amazon has benefited from the ludicrousness of the US patent system. While the idea of 1-Click online checkouts wasn't new back in the 90s, they were smart enough to patent the concept and enforce their rights as the patent holder.
As a result, anyone using a 1-Click checkout system has been paying them a royalty. That enforcement made barnesandnoble.com change their old 1-Click process to add more steps rather than pay the fee. But that patent expires today.