ok good, im not a unix expert (spent so much of my time on stupid windows) but "Disk Repair" did replaced some broken files on my system before... thats a fact... and they were .kext and .hid files. Also a friend (who definitelly doesnt know what he is doing in general) tried to edit some .kext files before (found some stupid tweaks i dont remember) which made dashboard any some other apps to crash. "Disk Repair" fixed those. So it does repairs system files. Its a fact, it happened.... And my f**ing sister is never gonna touch my computer again!
Disk repair only fixes problems with the filesystem.
It doesn't usually undelete files, because deleting
files doesn't usually cause problems with the filesystem.
You can use the "pkgutil" terminal command to find out
what installed the missing kernel extension last. Then
you can get the update, or installer off your OS X disk,
and extract the lost extension.
It's not terribly difficult to do if you know what you're
doing. The difficult part is knowing what you're doing