Doubleclick is a subdivision of Google.
As for "partners", Apple does the same. As their privacy policy states:
"
At times Apple may make certain personal information available to strategic partners that work with Apple to provide products and services, or that help Apple market to customers."
Just as many don't mind Google using their info to give personalized assistance services or notices, such as in Google Now.
This is not to say that I wouldn't love for this to be done locally, but having a central server do this across ALL my devices is pretty darned handy.
I don't think it makes a difference in the real world.
Yes, advertisers used to use our personal Apple advertising identifier to easily match us up, so Apple added that semi-bogus "Disable Ad Tracking" button. However, it simply sets a flag to tell the app developer that he
shouldn't use that identifier to track us. It does not create a hard stop, though, as the identifier is still quite visible. Most people don't know this.
Even changing it doesn't make an app forget who we are to begin with. Moreover, when Apple began disabling the UDID years ago, advertisers starting building an iOS MAC address id table.
There's always something that can id us.
For example, Apple bases its advertising slots on our location, demographics, media interests, and media/app purchase history. Anything that's in common can be used to help come up a personal match.
AI recently reported that... to help boost iAd sales... "
Apple's iAd division is looking to reinvigorate sales, and will soon allow third-party agencies to provide demographic targeting information to advertisers, including matching of phone numbers, emails and other data."
In other words, if advertisers really want to figure out who we are, they can likely do it. As if it matters. Not sure why people are so worried about personalized ads.