Steve has had pancreatic cancer for a while, so this is not a real surprise to the Apple community... but is definitely a tragedy. He stepped down from being the Apple CEO in August because he had gotten so sick, so I think he knew it was coming
"You have to trust in something- your gut, destiny, life, karma, whatever. This approach has never let me down, and it has made all the difference in my life." Steve Jobs 1955-2011