I believe it won't be illogical to hypothesize the role of success in Robin Williams' tragic death. Hollywood has a history tainted with a number of similar cases that support the assumption that fame and success could very likely drive celebrities to pathological degree of depression. Everything comes at a price, it is logical to assume some famous celebrities may find it difficult to cope with the pressure of their gigantic success and it could drive them to take their life away.
Success is associated with reward, achievement and fulfilment - the opposite of what fuels suicide. Success means accomplishing your goals and fostering your values in a way that makes you feel good about yourself and your life choices. People who commit suicide tend to feel depressed, hopeless, worthless and incapable. They do not have a positive outlook on life, whereas successful people tend to feel satisfied and ambitious.
It turned out that Robin Williams had Lewy Body Dementia, but the media didn't know this when it was first reported he committed suicide.
This can cause delusions and hallucinations which could've contributed to the suicide. Or alternatively he may have thought about how his mind would deteriorate slowly over his remaining years and decided he didn't want to have to live through that.
Depression can be a devestating issue for anyone, it doesn't really have anything to do with how he succeeded, but more in how he perceived himself and his life situation. He could have all the success in the world, or absolutely none of it, and it would have made no difference if his inner thoughts about himself were not happy.
Sure being in the spotlight is stressful, but Robin Williams has spent a lifetime dealing with addiction. Robin appears to have fought a losing battle. Success is a lot of pressure, absolutely, but I don't feel played any part in this recent tragedy. Robin had a problem that he just couldn't kick.