I know this is an old post, but I thought I'd respond. I cannot speak for either man, but I have a theory on why David started doing stunts.
As magicians, we leave an impression on those who watch us perform. Some will believe it's real magic.....others knowing that magic doesn't exist will usually be baffled, as if they just watched a puzzle that they can't figure out ("How did he make that object levitate?! I know it's not real, but how?!?")
So magicians create this fantasy in the spectators mind, or this "belief in magic", if you will. However, deep down, the magician knows it's not real. THEY know the secret. THEY know how it's performed. They may not get that same "special feeling" or HIGH that a spectator gets, especially if they've done the same effects over and over and over again.
So they need a new challenge. They need to do something that MOST people cannot (or will not) do. Hence, the physical challenges. The suspension in ice.....the underwater challenges, etc. These are things to challenge a magician, to recharge that belief in something greater than him.....to restore that "magic" within themselves.
Think about it.....the first time you learn a magic effect, a GOOD magic effect, you are excited. And when you first perform that effect for people, you can feel that same excitement and joy that your spectators feel. Now imagine that you do this effect 1000 times.......it may to become robotic to you. Automatic. You don't even have to THINK about what to say anymore, you just do it. Perhaps it becomes like a job to you......yes, it impresses the person you're performing for, but you've grown bored of it. So you need something that you can learn and challenge yourself. That is why I personally think some of these guys leave the illusions and tricks behind, and decide to push themselves to a physical limit. It still seems impossible or magical to many (there is no way I can hold my breath for 4+ minutes), but there is also something in it for the magician: a sense of accomplishment....of doing the impossible......of teaching themselves the power of self control and discipline.
What are your thoughts?