When I attended a university studying communications, many studies found that people gravitated towards content that were more likely to support their views and interests, verus being highly influenced by the content they see.
So, it is likely that if Fox has a more right-wing bent, and the other major news channels have more of left-wing bent, then that is why various camps are going to each channel. Fox is the only one with a right slant, while the others are splitting the left slant.
Years ago newspapers were the same way. They tended to be in favor of one party over the other. It's still true to some degree today.
I think its a good thing that we have Fox, CNN, MSNBC and other news sources, cause when one forgets to report something, or shows favoritism, the others are going to call them out on it.