The only reason he pleaded guilty was because he's probably already worn down at the prospect of having to defend himself thirteen times.  How long do you think that would drag on for, and at what cost?  By pleading guilty, he just wants to take his punishment like a man, and get on with his life, and also having to save the girls the ordeal of having his defence councel cross question them.  There is also the question of receiving a slightly lower sentance through saving court time.  The only real losers are his defence team who were hoping to drag the case out for as long as possible in order to make a killing.  I don't know how genuine half these cases are, but since this Jimmy Savile saga, there have been so many other cases all come to light at the same time, it's almost no longer front page news.