The following text is a theory as to why the Tragic Clown is alive in the Sims 1 and dead in the Sims 3. This also serves as a writing exercise of me, being the aspiring writer that I am. I often write about men who want to make differences to the world, so this is one of those:
The tragic clown was a man who was never taken seriously because of his bizarre ways, his stupidity, his clumsiness, and his poverty which led him to never make it to medical school. He pursued being a clown instead, hoping that even if he can't save lives with a scalpel, at least he can save lives using laughter, knowing that laughter is the best medicine.
So being the dork (and wannabe hero due to reading too many comic books, being easily impressed by the superheroes) that he is, some jerks pushed him to the pool. Because he is a hydrophobe who can't swim, he drowned. The only thing he ever did to make people happy in his life is to drown.
There were pictures made in memory of him by an artist, which were, in turn, bought by other depressed sims who needed some cheering up. Hoping that he can at least do something right, he haunted every picture with his spirit and appeared whenever he saw someone weep. Alas, all he can do is mope around with the depressed person he's trying to cheer up, being the clumsy man that he is who can't actually juggle, especially if the depressed person lived in a messy home, being the neat person that the Tragic Clown is. Even in the Hereafter 25 years in time, he still can't do things right. Even then, the only thing that he can do to make others happy is to become the object of insult. Also, since he is a spirit after all, the clown catchers can only take him away temporarily. The only way to get him off the house of the depressed sim would be burn the object that he haunts with his spirit (painting) or simply to just get rid of the painting in any way. He would also leave in dolor when he sees the depressed sim happy when he realizes his failure in cheering the sim up.
But then, all hope isn't lost for him yet. In another 25 years to improve his social skills and sense of humor, he takes on another form as a bunny, getting rid of his erstwhile clown image. He sought refuge inside his fuzzy suit and finally succeeded in his pursuit to become solace to the tragic souls like him, to make a difference to the world.