In an interview with Reuters, Alfonso Signorini, editor of Chi, also accused the British media of double standards for not publishing the photographs.
"It's a scoop and a big one ... I didn't have the slightest hesitation," Mr Signorini said.
The royal couple has started legal action against French magazine Closer which first published a dozen shots of Catherine, Duchess of Cambridge - formerly Kate Middleton - as she slipped off her bikini top while on holiday at a French chateau.
William's office has called the photos a "grotesque and totally unjustified invasion of privacy".
Chi, which like Closer is controlled by former Prime Minister Silvio Berlusconi's publishing company Mondadori, printed a 26-page special edition dedicated to the pictures on Monday after a weekend of publicity.
"The pictures are completely natural, they are not morbid and in no way harm the dignity or the morality of the people portrayed ... Plus, while the terrace was in a private residence, it overlooked a street from where anyone passing by with a good lens could have snapped them."
The pictures have rekindled memories in Britain of the media pursuit of William's mother, Princess Diana, who was killed in a car crash in Paris in 1997 while being chased by paparazzi. But Mr Signorini said the comparison was misleading.
"Diana was really hounded by paparazzi. Here we have a couple travelling on diplomatic trips and on holiday, I don't think they are subjected to the same psychological pressure," he said.
PLASTIC SURGEON COMMENTS
The photographs published by Chi are accompanied by what amounts to an anatomical analysis of the duchess's breasts by a plastic surgeon.
Britain's tabloid papers, fighting for their reputation after a series of scandals, have refrained from publishing the pictures, even though they are available on the Internet and in the pages of a tabloid in neighbouring Ireland.
Mr Signorini accused the British tabloid press of hypocrisy, saying the Sun, which has declared the topless photos off-limits, had no qualms running pictures of William's brother Prince Harry cavorting naked in a Las Vegas hotel last month.
He said he too had been offered Harry's pictures but had decided not to publish them because they were taken inside a hotel room and were "sexually explicit".
"For years we have been bombarded by the British tabloids that showed no restraint in publishing the content of wiretaps; I remember those between Prince Charles and Camilla Parker Bowles," Mr Signorini said.
"I understand these newspapers are under pressure now because they are in the eye of the storm ... But I don't understand their lecturing us, because they are not in a position to teach anybody, quite the contrary."
Mr Signorini said Mr Berlusconi, who threatened to sue an Italian and a Spanish newspaper for publishing pictures of naked or topless guests at his Sardinian villa, was not involved in the decision to run the photos. Mondadori is chaired by Mr Berlusconi's daughter Marina.
Mr Signorini said he had selected the two dozen photographs printed by Chi from 200 shots, but denied withholding more explicit pictures. He declined to say how much he paid for the photos.
The royal family should have shrugged the pictures off with a "so what?" rather than fighting in court," he said.
"People would have liked them more. Why do we all have to imagine that the royals wear a burqa or a one-piece swimsuit to sunbathe? They are human beings like everybody else," he said.