The razor example isn't analogous here, you can pretty much plan for when you need new blades. A farmer can't predict when the equipment will break down.
But the homework the farmer (or any purchaser - this same issue arises for medical imaging equipment, cars, busses, etc) should do is what will the service market looklike for his or her equipment after warranty. It's not easy to do this research - but the flip side is this: if the manufacturers have to sell unlocked service, they will charge more for the original sale. Economically speaking that may be better because the costs will be clearer.
Dealers may not have the parts, may not be able to provide the repair without calling in a technician, or may be located far away.
People are talking about R2R making things more expensive but the opposite can be true: service centers can often be lossy operations, so if you have to service machines at a lower rate (because people are DIYing it basically) it stands to reason you no longer have to price that in. Scaling out repair literature and part availability is cheaper than the actual service.
https://en.wikipedia.org/wiki/Information_asymmetry https://en.wikipedia.org/wiki/Bounded_rationality
I think really only a rabid free-marketer (as opposed to all economists as you imply in the first sentence) would expect the market to self correct on something like this.
This issue went to the supreme court on the question of whether a manufacturer could "monopolize" its aftermarket. https://en.wikipedia.org/wiki/Eastman_Kodak_Co._v._Image_Tec....
https://en.wikipedia.org/wiki/Eastman_Kodak_Co._v._Image_Tec....
FWIW, I had to add an extra period at the end to get the original one to get included as part of the link.
As a consumer, it is very hard to determine the restrictions that this imposes on ability to fix as it varies widely between devices.
I haven't seen any manufacturer label these items as a lease nor be upfront with the support lifetime.