I clip out only the the left as well. This was just how I was taught as my right leg is my stronger side.

Also, in Australia we ride and drive on the left hand side so your gutters, poles etc are on the left.

I have tried practicing unclipping and stopping with my right foot and it just confuses me. If I was in an emergency I would unclip left and then just tip over until my foot touched the ground.

On my first road ride I stopped at a set of lights, put my left foot on the ground and still had a soft fall to the right. I have no idea how it happened!