Another thing about the disappearing Jedi while we're on the subject. Thinking about it a little longer I think it was the Jedi way to commit suicide. Look at it this way, Obi-wan and Yoda were the only Jedi featured in the saga to disappear when they died, and they both died willingly. Obi-wan lowered his saber and allowed Vader to strike a finishing move. And in ROTJ, while it is true that Yoda was suffering from old age, I always believed that he willingly gave up his life. This idea is reinforced when Luke says "but Master Yoda, you can't die!", which means that Yoda is actually choosing to die.