I suspect that most legitimate PR agencies, media-relations departments, and publicists will be happy to comply with Google's guidelines. Why? Because, if the term "press release" becomes a synonym for "SEO spam," one of the important tools in their toolboxes will become useless.
Just as real advertisers don't expect their ads to pass PageRank, real PR people don't expect their press releases to pass PageRank. Public relations is about planting a message in the media, not about manipulating search results.