Maybe this move is not due to health issues. Perhaps Jobs believes that it is a good time to let somebody else be CEO just to show the shareholders that he is not as indispensable as they may believe he is. The fact that he will now be chairman of the board means that he will be in position to make a change should the new CEO not work out (though it seems like TIm Cook will be just fine).
Hopefully he will get a chance to smell the roses for a while. I might disagree with his politics but his performance with Apple over the past 15 years is legendary. Taking Apple from where it was in 1997 to where it is today is probably the greatest performance of a CEO in the history of business. I do wish him well.
Truly remarkable what Jobs has done with Apple. It was a dead company in the late ‘90s. His vision created a market that other tech companies have still yet to catch up with since.
I say this as a PC user for business, but an iPhone/iPod/iTunes junkie since they all came to market in the last decade.