What can you expect from an ad company ? Not tracking you would mean hurting their own business.
Google could easily switch to context sensitive ads but they don't because advertisers pay extra for "personalized".
Personally, I doubt anyone can really justify the added expense. The entire process is opaque to make any comparison difficult if not impossible. Just because I bought pet supplies last week, does it really make sense for pets supply ads to follow me all over the internet --- even on unrelated web sites?
But they can sell customized ads stating that they will be very well targeted regardless of current content. Which seems to be what advertisers want much more, and reason why facebook never opened up their apis to google+ IIRC, your social graph and its use is basically the only worthy thing on whole facebook.
It of course brings all this tracking evil, why google stopped being morally OK company etc. But the money are there.
>Personally, I doubt anyone can really justify the added expense.
The CPM of an ad is based off on auction. There is no extra fee for personal ads. The ad spot is just worth more and advertisers are willing to bid more money for access to the ad spot. If people can't justify the expenses the price of the ad spot will fall until people can.