Don't count on

Apple

(AAPL) - Get Report

chief Steve Jobs dashing onto the stage in a surprise appearance at the Macworld show this week.

Apple fans -- aware that Jobs was not giving the big speech -- held out hope that he might show up for a quick "hello" to put health rumors to rest.

But according to Jobs, his doctors have only now discovered the source of his weight loss -- a

hormone imbalance

-- so it's probably safe to assume he's looking even thinner than before. Jobs says he's begun a remedy to the nutritional problem but says that it may take until Spring to regain the weight.

The problem is that Apple, whose stock was rising $4.75 to $95.50 on Monday's news, is pretty much a one-man show, at least to investors. And this time around the company wants to avoid the scene-stealing impact Jobs' alarmingly thin appearance had in June, at his last public appearance. Last month, Apple announced that marketing chief Phil Schiller, not Jobs, would deliver the keynote speech. The announcement followed months of silence as concerns about Jobs' health flourished.

Transparency isn't exactly Apple or Jobs' forte.

For example, nearly two years after Jobs was diagnosed with pancreatic cancer, he revealed details for the first time publicly at a Stanford commencement speech that he'd been diagnosed with pancreatic cancer, had surgery and was fine. Before that, all Jobs and Apple ever disclosed was that he had been cured of a life-threatening illness.

Jobs had what's known as the Whipple procedure, according to reports. The surgery removes portions of the pancreas and digestive tract, and according to medical studies, most patients survive, however many experience weight loss and other ailments.

"Common problems after pancreaticoduodenectomy were weight loss, abdominal pain, fatigue, foul stools, and diabetes," according to a 2000

report

by Johns Hopkins.

Jobs has led Apple to some big hits since his return to the company 11 years ago, thanks largely to Jobs' uncanny ability to time product launches and choose designs that win with consumers. The company's sleek Macbook laptops were a hit at a time when buyers were shifting away from desktops. The iPod took over in mp3s where Sony's Walkman left off in cassettes. And the iPhone nailed the touchscreen trend just as phone giants like

Motorola

(MOT)

had run out of new ideas.

A strong vision, like Jobs has exhibited, would serve Apple well as it hopes to keep the home-run streak alive.

The PC industry

stumbled badly

in the past decade, and giants like

Dell

(DELL) - Get Report

and

Hewlett-Packard

(HPQ) - Get Report

are attempting a comeback that could change Apple's momentum. And in phones, the iPhone's early popularity now faces formidable competition from rival

Research In Motion

(RIMM)

and its BlackBerry Storm touchscreen device, as well as forthcoming phones from

Nokia

(NOK) - Get Report

and Motorola.

This means investors need Jobs, not just to survive, but also to deliver more hits at a time when challengers are working toward their own recovery.

Beyond Jobs, there isn't a clear successor.

Apple's management bench isn't all that deep with visionaries. The company's No.2 executive is operations chief Tim Cook. According to a recent

story

in

Fortune

, Cook comes across as a very effective behind-the-scenes manager, but maybe a bit too wonky for the center stage.

For now, word from Jobs that he's alive and getting better helps. But investors will continue to worry about Jobs' and Apple's health as the company enters more bruising times.