(Before I continue, a bit of disclosure. The company that I work for, Mac Publishing, does not run Macworld Expo. The company that runs Macworld Expo is IDG World Expo, a separate company that shares the Macworld brand name with Mac Publishing and shares the same corporate parent--IDG [International Data Group]. IDG's corporate structure splits different businesses into different companies, each with its own budgets and management teams. So while I'm the editor of Macworld, my business doesn't actually receive any money from the operations of Macworld Expo and isn't judged by the financial results of Macworld Expo. However, the owner of my business is the owner of their business, so we're cousins in the same corporate family.)
The timing of the announcement stinks. It's three weeks before the Expo keynote, and now Apple has decided to announced its plans not just for the keynote, but for the 2010 show? Why now? My guess is that the first announcement required the second. Imagine if Apple merely announced that Steve Jobs wouldn't be appearing at Macworld Expo. Immediately the Steve-Jobs-health speculation machine would whip into action. Jobs not appearing at Macworld Expo would be used as fodder to fuel a million different pieces wondering about Apple's CEO.
The announcement of Apple's "final appearance" in 2009 dulls that speculation a little bit. It won't go away--if you picked "three" in the pool to see how many comments it would take for someone in our story thread to speculate about Steve Jobs' health, --but in making that second announcement, Apple has changed the story from one about Steve Jobs' non-appearance into one about the death of Macworld Expo.
I don't know anything about Steve Jobs' health. And I really do hate idle speculation about the health of a human being. (Though I do believe that if he's terminally ill the shareholders ought to be informed. Otherwise, it's nobody's business but his own.) Who knows the real reason for the exit of Jobs from the keynote? There are a nearly unlimited number of reasons that don't involve the man's medical history. Maybe there simply weren't any earth-shattering products ready. Maybe someone at IDG offended someone at Apple. Maybe a product that was intended for release at Expo has been delayed, either for technical reasons or because today's economy would make it a bad time to launch a new product.
Apple doesn't perform on your schedule