It's here - http://store.steampowered.com/app/530620/ - not sure why they didn't use the "Download Demo" button that steam store pages sometimes have, such as - http://store.steampowered.com/app/418240.
Who needs logic, eh?
Take it up with valve.
Beginning hour isn't content that is in the game, and the way the steam store operates doesn't let you download a demo if you own the game already. Thus in order to keep it available to people who already purchased re7, they had to launch it as a f2p app and not a demo, requiring a separate page on the store.