Right, no one is doing mouse autopsies to determine the murder weapon but we don't wholesale kill humans in the quest for scientific research either. Don't discount a medical examiner's job as not being science. They aren't discovering new cells in the body but they are more akin to a GP doctor (versus a clinical research doctor). Just like your GP doctor, they can read the latest medical research, try new techniques and practices, and report experiences at conferences. Or they can work out of a 1950's handbook. But just like an engineer that can't be bothered to adapt to new technology, they are quickly going to fall behind their peers.

We don't remove the brain from someone murdered because they likely didn't give researchers permission to do so. Moreover, to study cells requires some skills not found at the coroner's.