Mac folks from all over converge on Macworld Expo to talk, see, be seen, learn, and hang with people you don't get to see all the time (like your family, who's sick of you talking about Macs). Macworld Expo is more about the conversations that happen between sessions and off the show floor than the vendor booths and the shiny new gadgets (those are important too, but when I struck up a conversation with the new 17 inch MacBook Pro, all it wanted to talk about was the new battery and my eyes glazed over).
This might seem obvious, but Macworld Expo can survive without Apple as an exhibitor and the media but it can't survive without the everyday Mac users that come to learn something and perhaps even to make a new friend or two.
Only at Expo!