said by Oh_No:
But it makes no sense that an interrupted download would brick it.
The download should download 100% and be checked before trying to install. You should not need an internet connection for installation.
As for power loss during installation, the only way to prevent that is to have two boot sectors or roms.
The 2nd boot sector or boot rom would still have fully intact old firmware/software on it that it can boot from if the 1st one is damaged or corrupted.
This kind of backup methodology could have been done for pennies per system and would almost 100% ensure no bricked consoles.
Many motherboard manufactures have two bios chips on the motherboard as a backup just to prevent being bricked on bios updates.
For security reasons, they could never use an old firmware image as a backup.