I have actually been electrocuted by one of those big capacitors in PSUs. It all really depends on how the current is traveling through your body ,ie. across your chest area is bad because of vital organs such as your heart and lungs.
Other factors could have caused his death such as mental shock or being surprised by the electrocution could have caused brain damage or resulted in a stroke. Also of note is that you should always wear an Electrical Discharge Wrist Strap that is properly grounded to the Earth.
It is tragic that people die from seemingless simple things such as computer parts.