I know it links to the page below, but I am not sure what animates the page pulling it dow - Joe Isaacson 2012-04-04 02:46
helixed's answer explains how they did it. However if you want to recreate the effect yourself have a look at using Parallaxjs rather than taking potentially copy-written code.
See the demo site: http://stolksdorf.github.com/Parallaxjs/
And source: https://github.com/stolksdorf/parallaxjs/
Edit: There is a bug with that website, try holding down the arrow key for a few seconds before letting go.