Mr Key was asked on Newstalk ZB this morning whether it was bad for democracy if there were fewer commercial television shows holding the Government to account.
He replied: "Its role in life isn't the hold the Government to account, it is to entertain its viewers and follow news stories. A great many of those don't involve the Government, some do."
Campbell Live is under review by TV3's owner MediaWorks as it revisits the 7pm time slot to try to improve ratings.
Mr Key said he had no inside knowledge about the review and any decision on its future was solely that of MediaWorks. Media reports indicated its possible demise was driven by commercial reality and low ratings.
"We live in a world where it is largely about commercial returns from what is a private radio station ... It's got a bunch of shareholders it needs to make a return to."
Mr Key said hour-long news bulletins were "struggling" even without tagging on an extra half-hour current affairs show.
"I'm not convinced it holds the audience. What you see is people zoning out."
Mr Key said half-hour bulletins were now standard in the United States and he believed that was because online news sites and social media meant most people were already abreast of the news before 6pm.
"That's the challenge those programmes are up against. That's why [TVNZ] went away from Holmes and Close Up to Seven Sharp. It's more breezy, magaziney show because people want light entertainment."
Mr Key also took a swipe at Labour's Clare Curran for her defence of the Campbell Live, calling her "that girl".
He said he fronted on the show when asked unless his schedule did not allow it or another minister was better qualified to speak.
"I always front up. It was a laugh when I saw Clare Curran putting out some statement from Labour saying how great Campbell Live was. Jeez, she must have no institutional knowledge, that girl, because it was Helen Clark who called John Campbell a 'little creep'."
That was after Mr Campbell took Miss Clark by surprise in an interview about the Corngate scandal in 2002.
Mr Key said Miss Clark refused to go on the show after that point. He said he would continue to go on it.
"Whatever his sort of views are, I'm there defending our corner and so as long as the show is operational I'll do that."
He believed there was enough investment in public broadcasting.
By Claire Trevett of the New Zealand Herald
