Lesson will indeed be learned, and in the future, there will be a number of children at risk, who are taken into care.
In fact, I would lay a month's salary as a bet that between the death of Baby P, and now, there have been a number of children who have been saved by social services, and or education authorities.
However, we won't know about these cases, because unless the parents/guardians have been prosecuted, they would not have made the news.
The sad fact is - kids are going to be killed forever. There is no foolproof way of stopping it, in the same way that there is no foolproof way of preventing any kind of crime.
It's just impossible.
Every once in a while, a child will be killed by his or her own mum or dad (or more usually...step dad).