I'm with the OP. I disagree that Russian Roulette is accidental death. "Died while playing Russian Roulette" pretty much covers it.
To me, it would have been most accurate to say Cory Heim "died of a drug overdose." I think accident makes it sound like it was a medical mistake. I would only assume suicide if it said intentional overdose.
Personal responsiblity is important. I think deaths due to risky activity can be teaching moments for those left behind. Saying this was an "accident" sort of downplays the fact that his own self destructive behavior played a part in it.
Drunk drivers can be sent to jail for "accidentally" killing someone. They don't do it on purpose, yet it is not looked at as an accident.
At the time of his death, it's important that he be remembered for the positive things he brought to this world. However, it's important that we learn lessons from his death as well and not gloss over the behaviors that caused it.