THe reason for the brick:
Wii system menu 4.2U bricks virgin wii's as well as modded wii's for the same reason.
It includes a faulty line of code that edits the boot2, something no update had ever edited before, to boot2v4. It's a simple short poorly coded code that sometimes causes freezing upon installation. Boot2v4 is already on LU64+ (serial number) wii's. This is supposed to make them unhackable, and it disrupts bannerbomb, eliminating the largest method of installing the homebrew channel, and is supposed to shut down when the HAXX ticket (HBC id) is presented for installation. They've already defeated this by changing the HAXX ticket to another four letter word. This boot2(v4) is what boots up the system menu when you turn your wii on. Now when this really terrible code starts installing it sometimes freezes the update, forcing owners to shut off their systems. Now your wii has no line of code anywhere in it's firmware which leaves it incapable of starting up, and just gives you a black screen, thus rendering it bricked. Funny thing is, for how bad Nintendo just f*cked up attempting to stop hackers, it's already able to be HBC'd, and bannerbomb is back with v2. If you have BootMii installed (wii loader on boot2) installed, and the update freezes, you can still run your wii.
The Big N is now replacing bricked wii's for free if they had no illegal software.
Nintendo really owes it's fans an apology, they screwed up normal users more than hackers, and those who updated safely got no new features except a craptastic boot2v4.
EDIT: Op please.