In reply to Sergey Biryukov.

In theory, this is right. However, in practice, it may happen that we need to hack WordPress core files to satisfy an extravagant, exceptional requirement, which was never considered in core, that no plug-in will handle, and that it's so exceptional that it makes no sense asking the WP community to add that feature in core (more, if it will take months to do, and we need to satisfy that requirement immediately). It may be wrong, but there may be no way around it.

I fully agree that it should be our decision to automatically upgrade our WordPress installations or not. The WordPress ecosystem is so big, that you can't really expect a one-size-fits-all kind of solution. The ocasional outliers must be allowed too.