Apple says that “News seamlessly delivers the articles you want to read in a beautiful and uncluttered format, while respecting your privacy, because Apple doesn’t share your personal data,”. What user data is shared with publishers. It is the same data that iAd shares?
In iOS 9 Settings >> News >> News and Privacy, there's a long text that itemizes the privacy protections (and limitations) related to collection and use of individual and aggregated data.
Regarding "Disclosure to Third Parties", it says, in part:
We do not share any of your individual data with third parties...
I'm pretty sure that the publishers themselves don't have any access to your personal data. It's likely Apple News collecting info on what Apple News articles you read and like, so as to present news stories and articles that you might like to read in the "For You" section.
Publishers get rich analytic just like any other web page you visit. The Apple News app is little more than a glorified RSS reader bundled with an in-app web browser.
In iOS 10, publishers will be able to distinguish Apple News users from other visitors to their website to a greater extent in iOS 9 due to a new User-Agent for Apple News 2.