So I was looking at this question: Did Obi-Wan need to sacrifice himself to Vader?
And it occurred to me... did Vader actually kill Obi-Wan?
At the end of the fight, Obi-Wan lifts his lightsaber and closes his eyes, clearly preparing himself to become one with the Force. Then Vader swings his lightsaber, and it passes through Obi-Wan's suddenly empty clothing.
Watching closely, it looks very much like Obi-Wan gives himself to the Force just before Vader strikes. Because of this, and with the visuals of Yoda's death, it looks like Vader never actually killed Obi-Wan.
Here's the fight:
Has this been discussed officially? Has Lucas or another source said that Obi-Wan did not die as a direct result of Vader's strike?
Answers from canon, legends, or Lucas preferred please.