I basically agree with you. However, if they are going to give the advice out to idiots, they really should make it idiot proof
A simple way to do this is a 2 stage BIOS with a starter PROM that does VERY minimal duty so i'ts hard to screw up. The starter PROM does only TWO things. 1. It tests one specific on-board USB port for a device with a specific code being present. If present, it will check for a partition containing a checksummed image that is not the same as the one already present. If the checksum validates, it will use that image to perform a re-flash maybe followed by a hard reboot. 2. Jump to the flash entry point.
Manufacturer provides the image file with integrated checksum, and an optional utility program for lamers to use that wipes the USB MBR, makes one partition the size of the file, and copies the file to that partition. If they want to prevent others from making these, they encrypt the image or checksum with something the first state boot PROM can decrypt.
The idea is an idiot can download the new image file and the USB transfer program. The idiot runs the program tells it where the file was stored (this may be hard for some idiots). When USB is complete, plug USB into the special on-board port (can be extended out to the back on some machines), and hard boot (reset or power cycle). It gets automatically flashed. If it fails, do over. Idiot may need a 2nd computer if yet another file needs to be used.
A smarter machine will have 2 flash spaces to keep a backup.
Manufacturers need to support idiots as those are now their largest customer base.