That is one of the many advantages to being the incumbent. Two others are that there are some things a President can unilaterally do by executive order - some of which can make a part of the electorate happy. They also get air force one.
As to the free air time, where it is more important is the general election. One major example I can think of is from 2004. John Kerry absolutely killed Bush in the first (foreign policy and national security) debate. They didn't even try to spin it - just conceded Kerry was an outstanding "debater" - trying to minimize Kerry's win. Then, mid week, Bush announced he would make a major foreign policy speech. He was given air time on all 3 networks and gave a speech that addressed many issues where - without a prepared speech (even with a wire which he may have had) he had been awful in the debate.
In addition, the debates at this time are doing two things. They are attacking Obama, but they are also attacking each other. This week's debate had some amazing moments. I don't know if Obama could have done better pushing Romney to show his own shallowness than Perry did on the question of the illegal immigrants that did his lawn. (What on earth was Romney thinking when he added that he told them he was "running for governor, for Pete's sake"? This is a loser on so many levels for Romney - it emphasizes how wealthy and detached he is - and shows his hypocrisy. His answer implies that if he were NOT running for Governor, he wouldn't care - which actually gets to Perry's point - he is a hypocrite on this issue.)
Edited to add this Politico snippet showing how Perry is now using that in
an official Rick Perry internet video :
FIRST IN SCORE – PERRY VIDEO TRASHES “MISLEADING” ROMNEY: Rick Perry’s campaign is releasing a dramatic one-minute video that portrays Romney as a deceitful flip-flopper and career politician. It highlights Romney’s response in Tuesday’s debate to Perry’s criticism that he once employed illegal aliens as landscapers through a contractor: “I’m running for office, for Pete’s sake, I can’t have illegals.” The tagline: “You can’t lead a nation by misleading the people.”
http://bit.ly/nnKITE http://www.politico.com/morningscore/1011/morningscore441.htmlThis is WAY more negative than Dean or Gephardt were to each other.