So what's up with Steve Jobs?

Speculation swirled in Silicon Valley and on Wall Street Wednesday following the previous evening's news that the 53-year-old Apple chief executive wouldn't be speaking at January's Macworld Expo in San Francisco.

Apple said Philip Schiller, an Apple marketing vice president, will deliver the keynote instead of Jobs.

Was the announcement a tacit admission that Jobs' health, long a subject of speculation, was failing?

Or was it an attempt to clear the way for a new generation of leaders at Apple, a consumer-electronics company that more than any other is identified with its CEO?

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"It begs the question of whether they're being fully transparent to investors," longtime Apple watcher Toni Sacconaghi of Sanford C. Bernstein and Co. told the Wall Street Journal.

The Silicon Valley Insider's Henry Blodget figured there could be only three reasons for Jobs to skip Macworld — a business dispute with Macworld host IDG, a delayed product that wouldn't be ready in time or, as he put it, "Steve is sick ... we regret to say that this also seems plausible."

CNBC's Jim Goodman tamped down the health rumors, stating "I can tell you that sources inside the company tell me that Jobs' decision was more about politics than his pancreas."

But the Valleywag tech blog, noting that the announcement came about as the result of a misunderstanding with a Business Week reporter, concluded the reasons were darker.

"I keep hearing apocryphal rumors that Oracle CEO Larry Ellison, who is among Jobs's closest friends, once broke down in tears and said, 'My best friend is dying,'" blogger Owen Thomas wrote.

Ever since he returned from corporate exile to retake the helm of Apple in 1997, Jobs has used his keynote address at Macintosh confabs to announce new products — the iMac, the iPod, the iPhone.

Even when there's not much news, as was the case at this past September's World Wide Developers' Conference, Jobs has still managed to spin whatever he has as something radical and life-fulfilling.

Jobs' terse announcement in 2004 that he had been diagnosed with, and then purportedly cured of, pancreatic cancer was a reminder that the world's top tech brand lies on the shoulders of one man.

Four years later, when a strikingly gaunt Jobs took the stage in San Francisco in June 2008 to announce the iPhone 3G, an Apple succession strategy had still not been disclosed.

An Apple spokeswoman dismissed Jobs' skeletal appearance at the result of "a common bug," and then later as the desired effects of an extreme vegan diet.

But it later came out that Apple's head honcho had been having digestive problems as a result of his cancer surgery.

Later in the year, Jobs bounded onstage at the WWDC, still skinny yet energetic and upbeat. A slide flashed the message, "The reports of my death are greatly exaggerated."

But tech watchers noticed that for the first time, Jobs shared the stage with Schiller and Apple Chief Operating Officer Tim Cook, leading the Gizmodo tech blog to predict that Jobs was planning an orderly exit.

In August, Apple stock took a hit when Bloomberg News accidentally ran a prepared Jobs obituary; a hoaxed CNN news report in October that Jobs had had a heart attack did the same.

Apple also said 2009 will be its last year exhibiting at the Macworld Expo, which is organized by the IDG technology media group.

The switch indicates "a shift in power going on at Apple," Piper Jaffray analyst Gene Munster told the Associated Press in an interview.

Munster said Schiller is one of two contenders to succeed Jobs at the company's helm; the other is Cook.

Apple said it was abandoning Macworld because the company has other methods for getting in front of customers, including its growing chain of retail stores. Munster said it makes sense for Apple to back out because it can generate just as much buzz by hosting its own product launch events.

But the analyst called that part of Apple's announcement insignificant compared with the news that Jobs will not be delivering the keynote.

"This is his baby. This is his presentation. It's his flock," the analyst said.

Munster said he believes Jobs' absence could mean that Apple doesn't have a big product to unveil this year, and that Jobs refused to give a newsless talk.

"I think that Apple could have done a lot to have made it so people wouldn't speculate about Steve Jobs' health," he said.

Apple spokesman Steve Dowling would not directly address questions from The Associated Press about Jobs' health Tuesday.

IDG World Expo, the IDG division that runs Macworld, said in a statement that it was disappointed Apple will not participate in the 2010 show.

Apple shares dropped $2.55, about 2.7 percent, to $92.88 in after-hours trading Tuesday, then spent the first half of Wednesday's session trading between $88 and $90.

The Associated Press contributed to this report.