Please refer to the following article from Wikipedia:
"All of the top four major leagues have had television contracts with at least one of the original "big three" U.S. broadcast television networks (CBS, NBC, and ABC) since those networks' early years, indicative of the sports' widespread appeal since their inception, continuing today additionally with FOX. Regular season games, as well as important contests such as championship and all-star games are often televised in prime time. In the last generation, fast-growing cable and satellite networks have taken a larger chunk of the major sports' pie. Three of the four major sports now have entire sports networks dedicated just to each of them. NBA TV launched in 1999, with NFL Network and NHL Network following.
Major League Baseball had announced plans for their own network, but then dropped them to attempt to start a national sports network with FOX. Those plans were dropped as well, after MLB and FOX failed to acquire a late season package of NFL games that went to NFL Network.
Comparing the sizes of television contracts, the NFL is by far the largest (reportedly $2.2 billion US for the 2012 season), with the NBA and MLB second and third ($500 million and $479 million respectively). The NHL is in a distant fourth place ($120 million), a disparity those who wish to exclude the NHL from the top four major leagues often point to. Since 1952 it has been broadcast on the Canadian Broadcasting Corporation's Hockey Night in Canada. The 2006 Stanley Cup Finals attracted 2.63 million viewer on the CBC.
The NHL began airing games on NBC starting in January 2006 and the NHL Network, currently only available in Canada, will soon be available to U.S. cable and satellite subscribers. In addition, the NHL broadcasts games nationally on Versus, generally on Monday and Tuesday nights. Many regular season games are also broadcast on regional sports networks (such as FSN), which can vary on contract worth by region or team."