About Blane's stunt, I think he's in awefully good condition for someone who's gone that long without food. By rights, he should be dead, so I suspect that the tube bringing him water has also been feeding him glucose and vitamins.
Well, the story goes that David lost his mother early on in life. And she was always his biggest inspiration who always supported him for his illusionary ways!
He lost her to cancer, and since then he believes there is beauty in pain and suffering.... which is why he performed this one.
And dedicated it to his mother.