- The idea is simple: advertisers have their ads placed in the most appropriate feed articles; publishers are paid for their original content; readers see relevant advertising - and in the long run, more quality feeds to choose from.
As I've said before, advertising in feeds isn't an obvious win. Excerpt-only feeds are already advertisements, advertisements of the full content of the article at the website. Layering ads on the ads will drive traffic away.
Those that do include the full-text of your articles in their feeds may find the feeds become the primary channel to some of their readers. In that case, advertising in that channel makes more sense.