I've found the Deere fluids priced competitively, and I use them as I've got better things to do then see if Brand X has the same specs Deere calls for.
The right fluids are cheap, engine and transmission repairs from the wrong fluids aren't.
Since the fluids are close enough in price that I don't get heartburn, I buy JD. Lets the parts guys know my face and when I need something they seem to take a little more interest.