The problem is that press releases often only give one side of a "story", while news articles often present it in a valuable narrative context.
E.g. a new product was announced because the old one used to catch fire. I mean the context isn't usually that dramatic, but there's often important information about a price change, or a response to previous consumer complaints, or how it fits into the broader product line, or is a response to competition -- all of which is much more valuable than anything in a press release.