Journalists aren't all Woodward and Bernstein. In fact, most of them aren't. They are, in the main, reporters. They report what they've been told, pausing only to package it up and make it more digestible to the reader. To hold the media in general to some higher 'you must be a domain expert to write about this subject' standard is to have a starry-eyed view of the world.
Science writers should have some understanding of the field they're writing about, though. If they don't understand the scientific details and none of their domain expert contacts are able to help, they should at least able to recognize the difference between a peer-reviewed article and a blog entry. Spotting unverified claims doesn't require any science knowledge at all.
Note that Woodward and Bernstein themselves weren't really any better — they did a good job sticking with the story, but were being spoonfed the acting head of the FBI was spoon feeding them everything!
<bracing myself for the downvotes>