The problem with absolutely certain is: you're counting on a lot of people to do their jobs really well. Crime labs to not f-up, prosecutors to turn over exonerating evidence, police to be thorough with the investigation, etc. Absolute certainty is a nearly impossible target. And then we'll still need the expensive and drawn out review process to make sure no one fucked up.
so, sure, there's a handful of cases where it looks like there may be absolute certainty. and then there's a bunch of cases where it was absolutely certain, and then it's found out the police botched the investigation and the prosecutors didn't hand over exonerating evidence.