Read this article -which explains how the McCanns won their libel case against the Express Group
The McCann Case - what issues does it raise
The article shows how the papers routinely edit and select material in order to present a particular viewpoint, and how easy it is to create a perception of someone in the eyes of the public. If that perception is misleading or inaccurate, this can do untold damage (think Max Mosely too) and it is difficult for anything to undo this peception, once the damage is done.
The McCann's chose to take the legal route and didn't go to the PCC at all. Perhaps they believed the PCC couldn't help them. Certainly, on a the question of taste and decency, there would have been nothing they could do. They could have ruled on the issue of defamation (libel) but would only have achieved an apology. Damages seem more suited to such a serious case, involving over 100 articles.
With freedom comes responsibility - this case arguably undermines the notion that the press is largely responsible and that self-regulation is enough to keep the balance in check.