It was problems with updating the plugins from inside the admin area that had me leery of any sort of update like this. It took me until about 18 months ago before I trusted WP's systems enough to start clicking on the "update now" link for plugin updates... before that I always updated manually with FTP because I'd previously never had a plugin update succeed without trashing whatever site I was working on.

I still won't do a WP update unless it's manuall, not even the minor ones. I simply do not trust all of the moving pieces that I know can hiccup at the wrong moment for an update a large as WordPress is (and it continues to expand in size).

I've had clients click the pretty little "update now" button and break all sorts of things that they sometimes felt they didn't need to pay me to fix. Having an update the likes of 3.5 or 3.6 done automatically, without a method to prevent it, would be disastrous, especially for people managing a lot of websites on different hosts for different clients.

If the WP team ever puts up a survey about opt-in and/or opt-out, I'm going to be in that very large group that's saying "Thank you, but No. Let us choose how best to update our websites ourselves."