I dare say it's possible that on some level, that could have factored into his decision to do it. He is ROBIN WILLIAMS afterall. He may go dormant at times, but Robin Williams is like a God. He WILL be a God now. He is the Charlie Chaplin/Groucho Marx of our generation.

And actually, this makes me wish I had seen all of his movies. And owned them. Or at least see Good Morning, Vietnam. I need to see if I can... find that somewhere to watch.
All true Williams fans should see Good Morning Vietnam...he single-handedly made that movie worth watching. With anyone else playing the role, the film would have been a crashing bore. I've always been under the impression that everything the character did on the air in the film was improvised. He was, quite simply, a genius.