Check, for instance, the credit page to any given Witchblade comic book; you'll see lots of names. And for any given issue, different writers and artists may be involved.
Check the credit page for the Witchblade Takeru manga, its just one writer and one artist. Berserk is basically just Kentaro Miura. Similarly, the ladies of Clamp do most of their own stuff.
This means that western comic books will tend to be brighter and glossier than traditionally black-and-white manga, even if their content can be somewhat more diffuse. Its takes a hell of a lot of man-hours to publish a top end comic these days.