The Prime Minister's comments will be seen as a further appeal to the 'grey vote' following last week's pensions shake-up. Labour has suggested that it could scrap some universal benefits for wealthier pensioners.
It added that it could not be right for millionaires to get free bus passes while public services were cut.
But Mr Cameron hinted that the payments would stay if they won the next general election.
Means-testing the benefits to ensure they were not claimed by affluent pensioners would save "a tiny amount" of money, he said.
Speaking at an event organised by Saga, the campaign group for older people, he said cutting the benefits would "introduce another complexity into the system".
He added: "We will set our policy for the next Parliament at the next election. I don't want to pre-judge that.
"But the only thing I would say is that people think you save lots of money by not giving these benefits to upper-rate, top-rate taxpayers."
He also suggested that the manifesto could include a pledge to raise the inheritance tax threshold.
Passing money down helped contribute towards "a stronger society", he said.
He added: "Inheritance tax should only be paid for by the rich. It shouldn't be paid for by people who have worked hard and saved, and bought a family house."
Most of the reforms will apply from next April, but a handful will come into effect on Thursday - to ensure those close to retirement do not miss out.
Under the changes, individuals with total pension savings of £30,000 or less will be able to take out the full amount, instead of the current £18,000 limit.
Yesterday, No 10 suggested it was relaxed about warnings from experts that pensioners would use the money to invest in property and inflate the housing market.
Mr Cameron's official spokesman said: "The Prime Minister's view is that it is right to give people greater choice."