Clearly, Google News has it's own algorithms and techniques in ranking stories and articles. Danny has one of the most comprehensive articles on ranking stories in Google News that I know of. But I spotted an interesting thread at the Google News Help forums about how possibly some stories can, over time, hurt your trustworthiness in Google News.
The person is trying to somehow communicate to Google that some of his stories are press releases and wants to tell Google not to index or add them to Google News. Why? Simply because he doesn't want to impact his "trusted source status" with Google News.
Inbal, the official Google News rep in that forum replied:
Thanks for your honest feedback. I encourage you to submit your press release hubs to our team; this should not have any implications on your current news site's ranking.
I believe you can even do this type of labeling in the new sitemap format for Google News, which is going to be required soon. Not sure why she didn't mention that as a solution.
But what takeaways do you get from this? Don't abuse your Google News access, because Google can drop your rankings in it easily.
Forum discussion at Google News Help.