John Deere by no means has a monopoly on farm equipment. If I was a farmer, I think this would make Deere completely unattractive. Heavy machinery like this has a pretty tough duty cycle and things break. Cost aside, Farmers often don't have the luxury of time to wait while they have a piece of equipment serviced by a limited number of authorized dealers. Having the option to use an independent mechanic or to (gasp!) fix it themselves would seem like a must have.
I'm not a farmer, but I do have a small Deere diesel tractor that I use for mowing, digging fence post holes, carrying around mulch/dirt/etc. I bought it years ago, but if I were in the market for a new one I now have a reason to avoid Deere.