Perhaps they felt that the amount of papers sold would outweigh any future consequences regarding Naomi Campbell.
Naomi did take The Mirror to court and eventually won herself the money she wanted, but lost what respect she had in the process after she was branded a "liar" by the high court, which was of course splashed all over the tabloids. This was The Mirrors way of saying, ok so you won, but not really. Because the media is the publics" information source as to what is happening in the world, they can choose to represent an issue or people in a bias way.
Leading on from this, newspapers are entitled to write an apology for any harm caused by an article according to the accuracy section of the PCC. In Britain, this apology can be of any size, even if the original harmful article was 15 pages long- The apology could be two lines long in size eight print at the back of the paper where no one would read it. In other parts of Europe, the apology by law has to be as big as the article that caused the harm.
An example of the effects of ownership and harassment is demonstrated in the Paul Burrell stories. Burrell, Princess Diana's former Butler despite making mistakes, was wrongly accused of the theft of many of Diana's possessions and as a result, harsh stories were splashed all over the tabloids. Burrell was hassled wherever he went in public by the press who refused to leave him alone. Because Burrell was represented in a certain bias way by the Press, this was the perspective the public saw too. As a result, the former Butler received death threats and was at the point where he simply could not leave his home.
The harassment section of the PCC has an asterisk before it, which is why Burrell was harassed to the extent that he was. The story was certainly in the interest of the public and it did sell papers, but to what extent is the harassment acceptable? Death threats was taking it too far, especially as the press were under the strong presumption that he was definitely guilty, when in actual fact he was not.