If you're Steve Jobs, an off day means people question if you've lost your magic. Apple and Jobs have long been joined at the hip. When he left the first time people rejoiced, but later begged him to come back. Why? Because his worth to Apple is in his presence.
Jobs is a figurehead with punch. It's apparent that he still has his fingers in the pie, but his real value, again, is simply being the face of Apple. The guy from the garage.
At a recent conference, Jobs had a lackluster performance and people are riding him for it. I think this is mostly because Jobs is a performer. They wanted a conference and the singer had a sore throat. Only, no one can really ask for their money back from a keynote - so they question if he's still got it.