Star Wars (the original) can be 'read' as a retelling of the Morte d' Artur, with Luke as the young Arthur, Obi-Wan as Merlin the Magician, etc. The light sabre is Excalibur...
A year or two later, the producers of the (bad) movie Excalibur went to pains to point this out; knights' helmets looked like Storm Troopers or Darth Vader; the young Arthur makes precisely the same moves with his sword as does Luke...etc.
--Boris
According to Lucas, on the commentary track for the latest DVD, the death of Obi Wan was not in the script, but was added in fairly late in production. It was not part of some grand design, but rather to accomodate the fact that he had nothing left to do in the movie.
Lucas does not strike me as a great intellectual (in the French tradition) so this sounds believable to me. Any time someone says they backed into a good idea by accident, I am inclined to believe them.