I really liked this mashup for 3 reasons: time to market, maintainability and business angle. Time to market: per John's blog the mashup was very simple to put together maybe a handful of days. Granted John is very talented but the end product is well worth 2 or 3 weeks of effort; still fairly quick to put together. Maintainability: I love the fact that the content is managed by AMZN and the NYTimes. With an automatic update this application requires no administration overhead. Finally business angle: by leveraging AMZN's associate program John now has the opportunity to profit from this application with minimum on going costs (e.g. hosting).
This example helps to underline the tremendous potential of the programmable web. A few dozen reusable services can potentially power thousands of applications and if these applications expose their own APIs then they become building blocks on their own to create millions of new services. I believe this formidable domino effect will create a new virtual marketplace with almost unlimited economic power.