Lines of desire?
Zeldman pointed me in the direction of this blog article, which describes a phenomenon in landscape architecture known as ‘Lines of Desire’, whereby ‘users’ take a shortcut across grass instead of using a walkway. This is analogous to web site maps, where the way a user wants to navigate somewhere may not be exactly the way the designer intended, a bit like what happened here. But it isn’t always best letting the user decide.