There are usually Windows updates once a month (at least big or critical ones), I have them activated, but I can understand those who disable automatic updates. For example, the one released last week took AGES to install on my PC after I restarted lol (I think it took around 30-45 min for the PC to completely restart, I'm on Win 8.1). Also, I remember some critical updates screwing up some stuff and not allowing people to boot their OS (mostly Win 7) just a few months ago. MS removed them a few hours later, but it was too late for some (I didn't have an issue, but I think I uninstalled them just to be safe).
So yeah, they are mostly safe and they aren't released too often, but I can see why some people are worried/bothered by them.
BTW, one thing that worries me about the Win 10 upgrade being free for "pirates" too, is that probably servers are going to get really hammered/slow during its release, so I'll probably wait a few months after it launches.