As an aside, the part about how ROMs are writeable via manufacturer tricks is what makes "amateur" reverse engineering of drivers a potentially costly affair.
You never know when you pop a hidden write trigger, and subsequently fill the ROM of your expensive hardware with garbage.
I recall reading about such a incident involving a DVD burner, where the OEM had reused a seldom used signal (stupid on their part, but still) as the trigger for a firmware update...
I believe that was Plextor drives, although I can't find a reference.
Anyways, smart manufacturers these days put some sort of a signature on the firmware (even just a CRC will do), and don't write updates to flash unless they have a good signature. That makes it much more difficult to accidentally trigger an update.
You never know when you pop a hidden write trigger, and subsequently fill the ROM of your expensive hardware with garbage.
I recall reading about such a incident involving a DVD burner, where the OEM had reused a seldom used signal (stupid on their part, but still) as the trigger for a firmware update...