How does a sphere work as a six sided die?

Why are square cube-shaped dice so popular when sphere and skew dice like the ones above look so much cooler? And according to Action Lab, they are just as fair as your run-of-the-mill boxy dice. Not only does this video inspire me to change up my board games with a variety of dice shapes, but it succinctly explains how spherical dice – which I didn't realize were actually useable – are made so that they work (and don't just roll off the table or land on a blank spot).
Tags: Video, Games, News, DICE, Sphere Dice