Come on. If you modify the device to work in a way it wasn’t intended (eg overclocked) you have clearly voided the warranty. This is what this is there to detect.
There were car makers voiding warranties when users replaced a tire. They gave the same arguments: Users modifying the car might do anything, so better give them no chance, as nobody could ever walk safely on the streets again.
Wiser heads prevailed, and e.g. the USA created the Magnuson-Moss Warranty Act. It is today legal to replace tires on your car. It is nevertheless illegal to make it non-street-worthy. If you stupidly damage your car while replacing a tire, you do in fact void your wararanty. If reality isn't clear enough, a judge decides. While streets might not be that safe, it is extremely rare that modified vehicles are part of the problem. The system works.
Why do we have to rediscuss all of this again? Exactly the same idea is applicable to software.
The important point is that the second of your changes is the one that voided the warranty: Replacing the tire to run in an unsafe way will void your warranty too. Modifying the ECU, on itself, doesn't do anything to the warranty.
And it is up to the manufacturer to prove your specific modification is unsafe. Claiming that some parts are inherently so complex that any change voids your warranty is legal bullshit for cars.
If I understand your argument well, it is that for cell phones the OS is so complex that any person on this planet should be declared unfit to make changes to it, except the manufacturer.
* First of all, the very audience of this site disproves this statement. Note the 'hacker' in hacker news.
* Second, I invite you to take a look to the garbage you find in most software powering our hardware. Someone going trough the effort to examine a device and create a modification is almost guaranteed to create better quality. There is something Darwinian going on here: Software mods, when they are supported for some time, give by their very existence away something of the persistent and qualified nature of their creator (otherwise they would not have been published).
* Third, the nature of software is that it is hard to create and easy to copy. Only 1 person has to create the firmware modification. The rest of us can copy it. This is exactly the reverse of the tire example and makes firmware mods a lot more easy.
UPDATE: After rereading, this post sees a bit harsh and a personal attack. So let me add that I have respect for your 2 posts. You provide a valid viewpoint in a reasonably toned, adult post. I also respond to more than can be found in your posts alone. I disagree with people downvoting you. I do however respectfully believe your viewpoint is incorrect and dangerous.
You are moving the goalposts, because we were talking about "changing the ROM", not about "changing the ROM and then doing something that will fuck the hardware up"
By the way, if you fuck up the CPU by overclocking it I guarantee they won't notice it because they will just throw the entire motherboard away. The subcontracted company that fixes your mobile (it's almost never the manufacturer) won't spend their time doing some CSI on it.
This is a lie sold to you to convince you to give up control to the manufacturers, to make a warranty a flimsy and easily discarded thing. Their products are getting lower in long term quality and reliability each year, but they don't want to take responsibility for them.
If you modify your cars engine increasing the pressure in the cylinders beyond what they are designed to handle you have voided the warranty, and wouldn’t be covered when the seals fail etc.
Your warranty covers the intended use cases. It does not cover you t do what ever you want...