In reply to Jeff Chandler.

I did about 50 Websites in the past years. An Update needs to be maintained by a human.

What if:
- The Plugin update is simply buggy.
- Your Theme depends on an already deprecated function of the Plugin, has been working through a couple of upgrades. The new Version will kill that function.
- You use a css selector that the Plugin also uses in the new Version
- Some javascript mess
- You violated the coding standards (modifying the core) in a way that doesn't affect security, like change the core. Example (question and accepted anwer by me): http://stackoverflow.com/questions/13460188/force-wordpress-to-create-thumbnails-of-same-size-as-the-uploaded-image

That's why I ultimatively decided to test updates on a mirrored copy of the Website only.
In other words, Wordpress would need to ensure the same functionality of the Front End, and a way back. Since a plugin update might also include changes in the database ... well, forget forced auto updates, and let people take responsibility and live with the consequences :)