The point is that when the firmware was locked down, it was vastly more difficult to bypass emissions restrictions. I'm not sure what you mean when you say John Deere was cheating the system. Arguably they were taking compliance more strictly before this ruling.
The emissions restrictions were meant to get the likes of Deere to design and use smaller, more efficient engines, not to keep doing whatever they were with a slightly more restricted fuel hose.
posit: are these considered 'road vehicles' in the same way that a car is?
> I'm not sure what you mean when you say John Deere was cheating the system.
Instead of selling tractors with more powerful, but limited motors, they should have sold tractors with less powerful motors and no screw. There is no need to do any of this in software. They were purposefully avoiding the regulation by telling farmers, "do not loosen that screw, or you'll break the law, wink-wink!"