Are they still gears if they are powered independently and the only connection between them is that they may come in contact without blocking each other's rotation?
They are driving each other. Although not well explained, the belt is just used to demonstrate how the angles are determined. This is a little clearer (although still hard to follow) if you watch the "Standard Gear Explanation" video first: http://www.youtube.com/watch?feature=player_embedded&v=lWuKl...
Imagine screwing in a screw. Rotation makes lateral movement. Imagine pushing in a sharp-ended screw into something soft. Lateral movement makes rotation. What I believe is happening here is that one screw is being rotated, generating a lateral force on the other screw, rotating it.
