There is also something that keeps being lost in this: identity and tracking are different things. Opt-out is a preference setting of an identity, and networks store this preference just like they store history and interests. By disabling 3rd party cookies and scripts, it disables the saving of any opt-out status as well, which btw, is actually mandated by certain laws and regulations so it's not all wild west here.
For anyone who wants an opt-out, here it is: http://www.youradchoices.com/