I have a number of Win 8.1 systems here at my business all up to date, and no Windows Updates have caused any problems, except for just one that had a momentary blip - the test virtual machine running Avast on which I tested KB3000850. It's been 100% fine since the fix.
A lot of people in general have screwed up computers. Who knows what junkware they have installed on them, and the people themselves actively screw them up - a great example is that many people seem to feel they need to use "cleaner" applications that indiscriminately delete things, as though operating systems need to be "cleaned".
Then when critical data is missing and a Microsoft Update fails, who do they blame?
Unfortunately, the mess that is personal computing today is so widespread that most companies now often take an approach where they try to discount reported problems as trouble caused by individuals rather than problems with their software. When they really do have product problems they tend not to get right to them until it's made painfully obvious by mass complaints.
Note that this very discussion has turned to Microsoft breaking things, yet why was the thread started? If Avast was doing something questionable in their software and Microsoft changed the OS - without breaking the documented rules of their APIs - who's really at fault?
Nobody's perfect, but Microsoft gets it right more often than they're given credit for.
-Noel