I don't think that google plans on picking a fight with Berkshire Hathaway, United Media, nor the AP, either.
I simply think that google will further continue devalue / punish any page rank value that is floated to the destination sites from press releases.
In short, google will end up punishing the small companies until it becomes "prevailing wisdom" to use nofollow links exclusively in your press releases.
Some press release companies that have a good reputation for generating media attention will survive.
Those companies whose only value proposition was as a way to float page rank will most likely not survive.
What percentage of PR companies fall into each category, I don't know. Companies that follow your exhortation to produce press releases that "stand on their own as news" will probably do fine.
I would venture to say that they are in the minority, though.