This isn't a foreign concept, either. It's how everyone started out. Google just thought they could charge more for ads if they also began tracking users so they could display higher-value ads that are supposedly relevant to a user regardless of the content of the page they are on. It turns out that they were right, and they are able to make more money doing this. Unfortunately for the rest of us, privacy is collateral damage.
There's no need for harvesting any data on the user, or tracking them across sites in this case.