Since the Force Immortality of Jedi is central to the destruction of the emperor, I felt like I needed some explanation for it. It's not a standard force power like jumping far or even lightening, it's something only Jedi can do, and even then only certain Jedi. And the Jedi must learn the trick, although it appears that force strength is also important. So maybe Lucas could have spent a few seconds on the trick at the expense of that pointless special effects thrill ride at the beginning of the movie.