
Rather than using a backlight as on LCD-based tablets, the Paperwhite uses a transparent light guide that directs light from four edge-mounted LEDs down toward the surface of the display.
The ratings are calculated by counting hits of the most popular search engines. The search query that is used is +"[language] programming"
More examples on Hanselman.com
The claim about data access speed is interesting, may be worth checking.
Forum discussion. Article at ACM Queue