The most important part of the article:
A license agreement John Deere required farmers to sign in October forbids nearly all repair and modification to farming equipment, and prevents farmers from suing for "crop loss, lost profits, loss of goodwill, loss of use of equipment … arising from the performance or non-performance of any aspect of the software." The agreement applies to anyone who turns the key or otherwise uses a John Deere tractor with embedded software. It means that only John Deere dealerships and "authorized" repair shops can work on newer tractors.
People are way too eager to sign away their rights.
In this case, it sound like it was probably because they had the choice between signing or (since John Deere appears to be able to turn the tractors off remotely — or at least, the article says the farmers worry that they can) having to buy a new tractor:
On average, be prepared to pay anywhere from $45,000 for a lower end used model to as much as $200,000+ for a farm tractor equipped with all the accessories that you need.