Cookies can only be set by web sites that you visit, so you don't have any cookies from web sites you haven't visited.
Cookies can come from sites that a person hasn't visited neither, and Facebook is tracking users of web sites they visit even AFTER they have logged out of FaceBook.
Safari likely recreates the cookies even after a user deletes them because of HTML 5, or perhaps with TopSites. Just started occuring too, like in the last few issues.
HTML 5 is bringing a whole host of spyware possibilities...
And of course Flash cookies are well known now
One has to use Firefox and the add-ons called Click&Clean, BetterPrivacy along with Ghostery, Ad Block Plus.
NoScript to prevent scripts from running automatically, one has to drag a "Temporaily Allow" button up to the toolbar to click it on "safe" sites.
I trust the independent developers working to keep their FF add-ons current to combat the latest privacy threats, as Firefox is more "the browser for the users" than any other.
It's getting insane trying to keep one's machine clean, and iOS users have no chance in heck as they are closed devices.
I am just going through this issue myself.
It seems that Safari 7.02 can't be trusted in erasing cookies.
I used to be able to use Reset Safari from the Safari menu, but I have 25 cookies re-appearing again and again even if I delete them, from Preferences/Privacy or reset Safari.
Is this going to be the reason for me to change browser?