Dave Winer on RSS ads in feeds without full content:
“To read the full article you have to click on a link and (listen very carefully now) see an ad as you read the article. In other words, the RSS feed is itself an ad, pulling you in to read a page with a big ad on it.”
This is true, but then again, Google makes most if its money by serving up pages of links with ads alongside, the links pointing to pages that in turn are often ad supported.
If double-dip advertising works for search engines why shouldn’t it work for feeds?