There are good medical reasons for autopsies as well. He might have had an undetected tumor, for instance, or other health issues. Not only does that help the family ("Oh that explains his constant headaches all of a sudden"), and if a brain tumor, it might explain his depression since it could have affected his moods, leading to suicide.
Also, it's good for doctors to know -- did it look like he had plaque buildup in his veins? Perhaps high cholesteral, and he was at risk for a heart attack. It's all good information for medical science.