Some early games had the joystick in the middle, with action buttons on either side (Berzerk, Scramble, etc). Also many, if not all, joystick-only games had it in the middle (ala Pac).
But it seems that the "primary" controls tended to be on the right for cp's with multiple controls; joysticks w/ buttons, joysticks w/ spinners, spinners w/ buttons, and so on. For example, on Tempest, the "primary" control is arguably the spinner, which is on the right and the zap buttons on the left. On Tron, the joystick would be the primary control and it is on the right with the spinner on the left. So the trend would seem to be that the control that needed quicker action or response tends to be on the right, where it would be easier for "righties" to respond to the game.
But, who really knows??
