Reading almost any document, given the small screen size of a handheld device, usually requires lots of scrolling.
Flicking pages as you read downward occurs very naturally, but then when you want to get back to the top to the table of contents, or gathered links (as on a news headline page), or the header on an email, or the starting point on a Safari web page, it seems like a long trip back when you have to flick and flick and flick to return to the top.
Fortunately Apple instituted a "Return to Page Top" design standard on the iPhone that Application developers adhere to.
Tapping on the topmost Stataus Bar (Red Arrow) causes the current page to auto scroll back to the top.
It's as simple as that.