That's right, the TV networks will do their job and look at what programming provides the best ratings and assign programming to different time slots and different channels accordingly.

With live sports especially, it's a "Wins Above Replacement" or "WAR" analysis like the baseball analytical metric -- the value is in replacing something in a certain time slot on a certain channel that would have a smaller audience. Using the example above, if an NHL playoff game is expected to draw 1.2 million viewers, the network will use that game to replace something else (reruns of PTI on ESPN2, or some game show on TBS, or whatever) that would have a smaller audience.