alanabit: whilst the cases you quote may have resulted in 'innocent' people in prison, I believe (without reading into it too deeply) that their sentences have been overturned because the forensic evidence would not now be sufficient to get a conviction.
However, had the police (or CPS) known at the time of the case that it could in time be overturned for insufficient evidence then they would (presumably) have sought more confirmatory evidence before proceeding with the cases.(possibly against the same people)
I am a great believer in the idea that "A man is innocent until proven guilty to the satisfaction of a jury of his peers" But I also believe that once found guilty, the 'presumption of innocence' can no longer be relied on, and a change in the law, or standards of forensic evidence, are not sufficient alone to overturn a jury's decision.

Just my personal view

CHEERS

Nigel