In this technical note about a recent eBook that I created, I wrote about the need to include a hyperlink (back to the page where you came from), on the target page. It seems that this is no longer necessary with an ePUB inside the iBooks app on the iPad/iPhone.
Why? Because in version 1.2 of iBooks, it seems that a history of the navigation pathway is kept while the eBook is open. This is then utilised to display (at the bottom of the page) a 'back to page x' hyperlink, when the navigation items are showing*.