The problem here isn't with the quality of the evidence produced by the lab, it's how that evidence was used/abused during prosecutions. Apparently the set policy of the crime lab was to withhold certain types of evidence that might be valuable to the defense.
State politics is as corrupt as it comes here in NC, and it goes right to the top. The state attorney general's office appears to be the place where future governors are groomed. The previous governor (Mike Easley - he's knee deep in corruption charges/allegations/investigations) was AG back when the crime lab was pulling this crap. (The crime lab falls under the AG's office, so it's the AG's job to set their policies.)
The current AG, Roy Cooper, the man now leading the charge to clean up the lab, is also gunning for governor some day. He's been AG for a decade, but didn't lift a finger to fix the crime lab policies until it became a hot political issue in the past month or so. Now that it's politically advantageous, he's going full speed ahead to the nearest camera to explain how he's going to make it all better "for the little guy".
Anyway, don't blame the science for this one. This is nothing but good ol' fashion political corruption.