Interesting theory on the cable news wars, brought to us by prolific media critic Michael Wolff  in USA Today (emphasis added):

The 2013 numbers are out, and once more, for 12 years running, [Fox News CEO Roger] Ailes … trashes everybody else in the cable news space, with an audience larger than CNN’s and MSNBC’s combined. …

Logically, there are too many cable news channels. The way to compete with Ailes is to combine CNN and MSNBC. But the structural anomaly of the business makes it not really about audience share, but about share of cable households — you get paid, by the cable carrier, for every household that might see you. And because of ideological appearances, every cable carrier that carries conservative Fox has to balance it with liberal MSNBC and middle-of-the-road CNN.

In that sense, Fox makes CNN and MSNBC possible — and profitable.