So far every time I have reinstalled Windows 8 for a customer on a store machine that it came pre installed with it never even asked me for a key and was activated when i booted up because of the SLIC. Thats why they dont put cd key stickers on them now.
As for the driver problem, the problem is in the registry. Something went wrong during the update and registry keys got screwed up. Not knowing which keys and how many makes it almost impossible to fix. If we knew which keys then we could fix it.
So the repair install would overwrite those keys and get ti working again. The problem with the registry is there is well over 1 million keys in there. The registry is a big database. And while my repair program does the best it can, there is a lot of keys that are machine specific and cant ever be added to the repair tool, and only Windows setup make those keys. Which make sense why MS has never come out with a registry rebuild tool.
So when the registry gets that deeply corrupted then a reinstall is the fastest and sometimes only course.
Shane