It's a tricky one
On the one hand, he is inextricably linked with Apple to the point where his health has a direct impact on the share price. On the other, he's just a bloke and perfectly entitled to take time off to look after himself without answering a load of questions.
In this case, I'd probably suggest Apple ARE out of order but not because they didn't publish every detail of Jobs' health problems. Any public company that has become so completely reliable on one individual without an obvious line of succession is in breach of it's duty to it's shareholders. I'd say the shareholders themselves should see this as a wake-up call and should be asking the board where the backup plan is?