There’s one big exception to that rule, however. Often, a reporter spends a long time getting a big and important scoop, which comes in the form of a long and deeply-reported story. When other news organizations cover that news, they really do have to link to the original story — the place which did it best. Otherwise, they shortchange their readers. A prime example came last August, with Matt Taibbi’s 5,000-word exposé of the SEC’s document-shredding. Anybody covering that story without linking to Taibbi was doing their readers a disservice.
As a result, like most things online, it’s very dangerous to try to come up with hard-and-fast rules about such things. In general, it’s good to link to as many different people and sources as possible, because the more links you have, the richer your story is. On the other hand, the journalistic web is full of garbage hyperlinks — automated links to irrelevant topic pages, for instance, or links to an organization’s home page when that organization is first mentioned.
As for crediting the news organization which broke some piece of news, that’s more of a journalistic convention than a necessary service to readers. It’s important enough within the journalism world, at least in the US, that it’s probably a good idea to do it when you can. But most of the time it’s pretty inside-baseball stuff. And in the pantheon of journalistic sins, failing to do it is not a particularly big deal. What’s much more important is that your reader get as much information as possible, as efficiently as possible. Which means that if you’re writing about a document or report, you link to that document or report. Failure to do that is a much greater sin than failure to link to some other journalist.
So while sometimes the failure to link is unavoidable, I look forward to a time when journalists face much more criticism for not linking to primary documents than they do for not linking to some other news organization which got the news first.