I don't think it is necessary either.
Do you feel a news site using AdSense can't be objective when talking about Google, or the products that appear in the ads?
Mediapart is not about news on the latest iphone nor your average tabloid, they release news about political corruptions, large companies lobbying, and the like. Not having pressure from any company, or government, or political side is why they have subscribers (myself included, fwiw, disclaimer here).
This wouldn't happen because a news org would never recover the cost of an actual investigation from AdSense impressions.
And even if they did, 100+ other websites will just rehash the first paragraph, write a catchier headline, and come out with a positive ROI...and stay in business.