Aren't a lot of the pics sent in to companies like Boston Globe and Nat Geo from freelancers? So they get the opportunity to just pick and choose the best, most compelling pictures of the bunch.
I mean, you can only have so many staff photogs on payroll, and there are a lot of stories to cover around the world (though I don't doubt at least a couple/few staff photogs would be dispatched to such an immense story as Haiti).
edit: If you looks at the credits, a lot of the images come from newswire services like AP and Reuters, as well. Certainly Boston has some staff and/or contracts a photog that uses a newswire service for assignments. But what seems to set them apart is they must have some competent editors (or whatever) who know how to pick photos for a combination of story telling and technical mastery.