"Today, if a Windows user finds that an update breaks something that they need, they can generally refuse that update for an extended period."
Please tell me what kind of average Windows user checks the internet for any indication of an issue with a patch? We are talking about users that refuse to set a password on the only account on the system, that is also the administrator account. Users that never update Java, Flash, etc.
If someone is tech savvy enough to hold off patching until the industry has vetted them, they wouldn't be using the Home version regardless, they'll pay the 99 dollars to upgrade to Pro.