How can you leave in the fat and have it still be a powder that isn't a sticky gooey mess? I wonder if the difference between .5 and 1 is perhaps just a matter of rounding.

I would imagine cocoa powder is similar to peanut flour. If you don't de-fat peanut flour, you have peanut butter.

http://www.howstuffworks.com/how-chocolate-is-made4.htm

There is a taste difference in cocoa, but I think it is due to processing (roasting, dutching, etc).