Read before you scroll. Don't just scroll to the images.
http://www.thesneeze.com/mt-archives/000707.php
I can see why they have left and right and not just "half" though...
You need to be able to specify more than one topping on each half.
So if you want peppers and onions on one half and pepperoni on the other, you need a left and right- not that they throw all the toppings on one side and leave the other just cheese.