Apple recently changed the way Safari behaves when you scroll down. Prior to iOS 7, the address bar and controls would hide themselves automatically once you started to use the page. You could force them to reappear by scrolling back to the top.
As part of the big move away from skeuomorphism they changed this sensible arrangement. Now when you scroll the address bar shrinks to show the host name, but never really disappears. This is unnecessary and detracts from the user experience in my opinion. In effect, you can never go “full screen.” <frown>
There is a work around that has some advantages over just browsing or bookmarking the site. If you save the site to your home screen iOS will treat it as a web app. In this case the browser controls disappear completely. Nice! An extra step but worth it!