It seems this works only for Focus 1.3.
Since there are no OEM updates with this update, only the OS version number changes. If there were OEM updates, then this method of updation will brick the phone as the OEM updates are not for this mobile.
That is partly correct. Indeed there are no OEM updates in 8107 (I won't revert to 7740 to check anyway changes in firwmare) but it would not brick the phone if there were. With the LG settings, Zune still saw my phone as Samsung since it needs the Samsung driver to connect through.
Why can't people update? Simply: because carriers don't allow the update to go through immediately, but gradually. So you need to change the carrier to one that delivers the update. It won't actually matter what phone you have, you need to get the notification in Zune, then Zune will see what phone you have and connect to MS servers to download the update. And since the registry changes were reverted, it reflected your current phone, so it won't brick it