"You mean that in a newspaper it's not the newspaper saying it, but only the "contributor" (journalist) writing it? Sure, sometimes it happens (i.e. op-eds) and the reader is usually explicitly warned. AFAIK, the newspaper is still responsible for what it publish."
The journalist is employed by the newspaper, one way or another.
If a "newspaper" existed whose whole shtick was that pretty much anybody could put a piece in it, blog style, I doubt the newspaper itself could be held responsible.