Someone once told me their theory on how Anakin gets his wounds. Akira Kirosawa has greatly inspired Lucas. If you don't believe me, there is a large thread on it somewhere around here. Anyway, I believe Palpatine gives Anakin at least 75% his wounds. Anakin is to destroy Obi-Wan but lets him go ("You should not of come back"), thus Palpatine uses force lightning on him. But since Anakin is "the Chosen One," he survives. Palpatine sees Anakin's power and has him reconstructed. This would make Darth Vader forever Palpatine's slave because he fears him. And in Return of the Jedi (which I watched last night) Vader sees his son going down the exact same path of test and torture. This drives him to the edge causing him to kill Palpatine and finally brings "balance" to the force. Therefore, he has completed his destiny and can no longer live, even with life support.