Dave Zatz, the editor of Zaznotfunny.com and writer for a number of tech sites including The Verge, Engadget and PC magazine, tweeted this earlier:
What does this mean? Who knows!
Like Zatz says, this could just be "professional courtesy". Executives could be showing up because they are partners with Apple, and Apple asked them to be on hand. Also, this is a major event for Apple and it marks the start of a new era. If you can be on hand, you might as well.
Or, if you want to get excited... it may mean that Apple might announce something related to the TV business. Apple has long been rumored to get into the TV business, but so far we have nothing to show for it. A report from The Information in July said that cable companies were "dragging their heels" when it came to agreeing to partner with Apple to allow it the rights to their content.
Apple is already expected to unveil the iPhone 6 today, along with a smartwatch, which many experts have already dubbed "the iWatch".