Those are hardware mechanisms backed by software that tells the hardware mechanisms what to do. You have a lot of trust in them!

I recently discovered that my Windows machine wouldn't boot because my boot sector had been replaced with some random XML. That's exactly the sort of thing that hardware protection is supposed to prevent - nothing during a normal run of the OS should be writing to the boot sector, at all.

Do you restart your OS when it oopses and kills a process? Linux in fact catches bad memory accesses from kernelspace and attempts to just kill the current process and not the whole kernel.