The keys 'hjkl' have a special meaning for a lot of UNIX users. They are used to move around inside the vi text editor, and have been used by loads of websites as keyboard shortcuts to move around inside a page. One of sites I visit often that I uses them is The Big Picture of the Boston Globe. Inside each article, you can navigate between photos using 'j' and 'k'. Try it.
The source of this convention started with Bill Joy, the creator of vi. The reason for this particular set of keys is because Bill Joy used a ADM-3A terminal, and the keyboard has cursor arrows printed on those keys.
You can see a big picture of the ADM-3A on Wikipedia. Zoom in on the keyboard to see the arrows.
Nothing like a bit of geek archeology...