I think we need to approach this question with a multi-faceted answer that acknowledges the role that society and in particular capitalism and the American dream played in Willy's suicide. To ignore these contextual factors is to be blind to significant influences on all of our lives. At the end, Miller seems to be commenting more on a system that makes Willy think the only thing he can do to salvage anything out of his life is to kill himself because the money he would earn for his family would be worth more than his continued life.
I agree with a lot of the above. Yes, Willy did end his own life, so at the surface level he is responsible for his own death. But I've always thought it much more interesting to analyze the role society played in his death as well. It's a good way to read the play, with a focus on a man like Willy Loman vs. society. The evidence piles up from the very beginning, and the scene in Howard's office is especially pathetic in regards to this subject.
Willie was responsible for his own actions, so ultimately, he made a choice to end his own life. Technically, he IS responsible for his own death, yes. However, as others have mentioned above, there are a bevy of circumstances that fell into place to cause him to make this choice.
I would imagine this depends on your view of how responsible we are for our actions. Despite all his "dreams," Willie finally lost hope; this loss of hope is probably what leads to most suicides. He invested his whole life in a career that was probably an illusion. He invested another part his life in Biff. But when Biff caught him in a "tryst" in Boston, Biff realized that the Dad he had idealized was, in fact, a man. It destroyed their relationship, one of the mainstays of Willie's life. The little things that keep falling apart during the story foreshadow the falling apart of Willie's last hopes.
If Dreiser had written this play, Willie would be a victim of chemisms, drawn like a moth to the flame of dreams that were not worth of him, and his resonsibility would be attenuated. If you view humans as responsible for all the decisions in their lives, then who else is there to blame? As I said when I started, it's up to you.
The is at the core of the long running discussion of whether Willie is a tragic or a pathetic hero. This might be a good thread to start ....
There really isn't one person who is to blame for Willy's death. There are a combination of factors that led Willy to kill himself. Willy was consumed with his own conception of the American dream; the play chronicles his sprialing downfall. He cannot initially come to terms with the fact that he is no longer a successful salesman, that his sons are not amounting to much, and that he has not been faithful even to the one person who loved him no matter what, his wife Linda. His decision to kill himslef may have resulted from a confluence of the above factors in his life. Willy is ultimately the one who kills himself, who makes the decision, who acts out of hoplessness and desperation. It is his inability to see past the materialistic side of his American dream that leads him to his destructive action, his inability to remember the preciousness of life. He decides that since he can no longer provide for his family and future, that ultimately he is worth more dead than alive. In fact money may be what actually caused his death, or the pursuit of money for the benefit of family and for the protection of his family's future. The reality is that Willy's family needed Willy, not the money from his insurance policy.