Windows updates don't just "break" your PC. It's probably software on your PC that is not compatible with an Update that causes the reboots or BSOD or whatever the issue may be.
For the most part this is true, but I've also had client computers where everything else is fine, but a Windows update managed to put them into a boot loop, or dropped out their sound, or messed around with the LAN drivers or confused Windows update itself. **** happens, they can't possibly test for every software and hardware combination under the sun.
I am a System Administrator and I update hundreds of computers ranging from XP to Windows 7 & 8 and we don't see this effect anywhere to what you describe.
Not meaning to be antagonistic here - your experience is completely different. You have a controlled environment where the users probably don't have much in the way of Admin or Power User rights to begin with and if you have solid policies, you test updates on a few clients first before rolling them out completely. Personal client computers change on an almost weekly basis and its those machines that see the majority of issues. Finding the root cause of the issue usually takes quite a while because you're not familiar with the setup or what files are on the system.
In my case, my personal rig failed to run through the Windows 8.1 installer because a lone piece of software was causing the update to crash and forced Windows to retrace its steps - turned out it was the Steelseries Engine drivers at fault and I spent weeks figuring that out.