I don't believe that you are missing anything.
The thickness factor system is just a way of extrapolating from one size of pizza to another so that the finished products have essentially the same characteristics. The thickness factor is sometimes called a "dough loading factor". I don't know where it originated but I first heard about it years ago from writings by Tom Lehmann, of the American Institute of Baking. In the example you used, the thickness factor is 0.10. That is the value that I often use for the NY "street" style although a value of 0.085 is perhaps closer to what is typical for a NY style. Other types of pizzas typically have other values, as I noted a while back at Reply 1 at http://www.pizzamaking.com/forum/index.php/topic,12243.msg115759/topicseen.html#msg115759
. I suppose that if pizza crusts were made of some other edible substance besides flour, the range of thickness factors would be different. FWIW, I have never seen thickness factor values for gluten-free crusts. But values could be calculated from different gluten-free crust products.
You can read more about how the thickness factor (dough loading factor) is used from this article by Tom Lehmann himself: http://www.pmq.com/mag/2004november_december/lehmann.php
. The dough loading factor concept also works with items like sauce and cheese. Tom Lehmann describes how to use that method for cheese at the PMQ Think Tank at http://thinktank.pmq.com//viewtopic.php?f=6&t=6169&p=38621&hilit=#p38605
. He also uses that method for sauce but I believe that it can be made to work for various toppings also. The value of the loading factor method to a pizza operator is that all of his pizzas should have pretty much the same finished characteristics. Sometimes operators will also discover once they apply the dough loading factor to all of their pizza sizes that they were using disproportionately large amounts of expensive items like cheese on their various pizzas.
All of the dough calculating tools (at http://www.pizzamaking.com/dough_tools.html
) have the thickness factor concept built into them, although there is also a dough weight option for those who prefer to work with dough ball weights form the outset.
EDIT (1/25/13): Since the link to the above Lehmann article is no longer operative, see the Wayback Machine link to the same article at http://web.archive.org/web/20110404180542/http://pmq.com/mag/2004november_december/lehmann.php