Steamy scenes alone in a movie cannot pull the audience to cinema halls, for the most popular movies at the box office are those that can be watched with the entire family.
M, PG and G-rated movies account for 70 per cent of this year's box office takings.
And the most lucrative classification is M, which accounts for 320 million dollars in ticket sales so far this year, or 44 per cent of the box office.
Earlier, M was recommended for those aged 15 or over, but the age limit has been dropped and the classification now suggests material suitable for "mature audiences".
The top films so far this year, Transformers: Revenge of the Fallen (40.3 million dollars) and Harry Potter and the Half Blood Prince (40.3 million dollars) are rated M.
Both the films were screened during the July school holidays and have been popular with families.
The next most lucrative classification is the PG rating, with 19 per cent of the box office so far, or 200 million dollars.
Ice Age: Dawn of the Dinosaurs (29.8 million dollars) and Monsters vs Aliens (20.6 million dollars) are the third and fifth most popular films this year.
Just one restricted film edged into the top five-the broad comedy The Hangover (MA 15+)- that grossed 21.4 million dollars.
Motion Pictures Distributors Association of Australia general manager Rob Mages said that the popularity of unrestricted films could be seen around every school holiday period when the box office spikes.
"Kids are out looking for entertainment and exhibitors certainly take that into account," the Courier Mail quoted him as saying.