After much research, I just purchased a Staub "5 quart" oval cocotte.
In the midst of my research, I discovered by checking Staub's website for the stock number, that some places list the ,same cocotte as having 4.5 quarts capacity, and some 5. I found the same thing with a few of the other sizes such as 6 3/4 quarts and 7 quarts.
Here's an example taken from Amazon of the 4.5/5 quart models.
Listed as 4.5 quarts, item model number: 1102942 http://www.amazon.com/Staub-Quart-Oval-Cocotte-Lemon/dp/B0028Y5RNQ/ref=sr_1_6?s=kitchen&ie=UTF8&qid=1286578124&sr=1-6
Listed as 5 quarts, item number: 1102925 http://www.amazon.com/Staub-Quart-Ova...
The Staub website lists each of these models as having a 4.5 capacity.
I wound up purchasing what is described as a "5 quart" from Amazon and am happy with the color, price and what I assume is really, a 4.5 quart cocotte.
I didn't contact either Amazon or Staub about the discrepancy, as I think both are pretty reputable and it just perplexes me. I know there has to be a valid reason for the discrepancy, but right now, it's elusive to me. I thought I would as you very knowledgeable folks if you can tell me why this is?
I contacted Staub USA directly because I had some of the same questions. Apparently they do make slightly different sizes for places that feature "exclusive" Staub items such as Williams Sonoma. They told me that sizes as well as colors can be exclusive and differ from what Staub offers in their catalog.