Labour calls for Jeremy Hunt to be investigated for deliberately misleading parliament have been defeated in a Commons vote.
Despite the absence of Liberal Democrat MPs the Conservatives won the division by 290 votes to 252, a majority of 38.
The Lib Dems' abstention, outlined by leader Nick Clegg to MPs at a meeting in Westminster earlier this week, has frustrated Conservative MPs keen to shield their embattled culture secretary from further criticism.
But Mr Cameron sought to shrug off the situation in prime minister's questions. He suggested the Lib Dems were trying to lay out the difference between their limited dealings with the Murdoch empire and the unhealthier relationships cultivated by the Labour and Conservative parties.
"To be fair to the Liberal Democrats they didn't have that relationship, and their abstention... is to make that point. I understand that," the prime minister said. "It's politics!"
Mr Cameron has already declared himself satisfied with Mr Hunt's dealings with News International before and during the period when Mr Hunt had a quasi-judicial responsibility to rule on the Murdochs' bid.
But Labour pressed the issue with its opposition day debate. Its motion called for Mr Hunt to face investigation over whether he breached the ministerial code on giving accurate and truthful information to parliament and responsibility for his special adviser.
Speaker John Bercow raised eyebrows when he ruled that Labour MP Chris Bryant's accusation that Mr Hunt had lied outright to parliament was in order. Usually the Speaker rules such allegations to be unparliamentary and asks for their withdrawal.
"Evidence of not complying with the code can be drawn from the fact that the misinformation provided was emphatic rather than tentative, was repeated, was not corrected when fuller information was available or was calculated to deceive for political advantage," Mr Bryant said in his speech during the debate.
"I believe there is prima facie evidence that all these things apply to the secretary of state for culture, media and sport."
He did not produce any new evidence that this is the case, however.
Meanwhile Sir Alex Allan has written to Mr Cameron backing the prime minister's position - as Mr Cameron made clear at the despatch box this lunchtime.
"The fact that there is an on-going judicial Inquiry probing and taking evidence under oath means that I do not believe that I could usefully add to the facts in this case though I remain available should circumstances change or new evidence emerge," Sir Alex wrote in a letter sent earlier today.
Ed Miliband responded by quoting Lord Justice Leveson explaining that he could not rule on the question of whether Mr Hunt has breached the ministerial code.
The Labour leader accused Mr Cameron of refusing to refer Mr Hunt because he is "scared the culture secretary won't be cleared".
"It's not about the culture secretary's judgement - it's about the prime minister's judgement which is so badly flawed even his deputy won't support him," he added.
The Liberal Democrat leader offered surprisingly strong support of the culture secretary in his evidence to the Leveson inquiry, however.
Commenting on the way Mr Hunt handled the BSkyB bid, he said: "I think he's given a full, good and convincing account to this inquiry."
Lib Dem strategists will be hoping today's abstention will help distinguish the coalition's junior party from the Tories.
"We'd always had a different view," Lib Dem deputy leader Simon Hughes told the BBC News Channel.
"We had a view if there were any issues remaining after Jeremy Hunt had given evidence... they should be referred for an inquiry, and therefore we can't support the Conservatives on what was a Conservative-only decision."
Mr Hughes explained that the Liberal Democrats were not prepared to vote against the motion because Mr Cameron's decision has already been taken.
"The Labour motion is calling for the reference now by the prime minister to the independent adviser - this is after the event," he added.
"The decision has been made a few weeks ago. There's no point Labour trying to rewrite history."
Another Lib Dem MP told politics.co.uk that an abstention was judged the most practical route because it was the easiest for the parliamentary party to unite behind.
Shadow culture secretary Harriet Harman said before the debate that it represented an "important opportunity" to underline the need for secretaries of state to be "transparent and truthful to parliament".
"I think members from all sides of the House will want to be sure that this issue is not simply swept under the carpet," Ms Harman said.
"Misleading parliament is not just some outdated constitutional issue – it matters."