The reason that this is fair is that the smaller parties have very little support. There is very little reason that parties with little support should get anywhere near to the same kind of media exposure that the major parties receive. It does not make any sense to force the media to essentially give away their product (air time) to candidates in whom the public has little to no interest.
For example, let us look at the last presidential election. President Obama was reelected with almost 66 million people voting for him. By contrast, the third party ticket that did the best was the Libertarian Party. This party candidate won about 1.25 million votes. This means that President Obama and his Republican challenger, Mitt Romney, each got about 50 times the number of votes that the Libertarian candidate got.
Of course, there is some amount of “chicken or egg” to this. Perhaps if the Libertarians had gotten more publicity they would have gotten more votes. But they surely could not have come anywhere close to the major parties. Therefore it does not make sense to make the news organizations cover them. If a third party ever gets anywhere close to being viable, it will get plenty of coverage (as the “Tea Party” did as it arose).