Much of the magic you see on TV is not live. What you are viewing is from carefully calculated angles and shifts in the camera, such as in the instance of levitating. Usually the person being levitated wears a harness under his/her clothes and they are lifted by very thin wire against a very bright sky, to keep them out of view. Every once in a while you can catch shows on TV explaining how certain tricks are done, such as: levitating, making objects disappear, submersion in water for long periods of time, being decapitated, escaping restraints, etc. It's all a complex system of hiding your actions from view.
David Blane is all different kinds of strange, lol, but he is very amusing.
Kikuyo, you're somewhat right. The only magician that exploits camera tricks ( along with fake audiences ) is Criss Angel. David Blaine is more of the practice type that really puts work into it, but he does do SOME camera tricks.
The balducci levitation ( which is what Blaine is really famous for ) is actually very simple and can be done in real life. Angles are of extreme importance in a lot of visual effects. But, the most important part of magic is usually the patter, ie., the story that goes along with it, and how you present the trick. Blaine is lacking in his patter, but he makes up for it with a lot of good visuals.
David Blaine also does a lot of endurance tests. It's not really magic, it's just extreme will power.