Simple because you can copy and paste this code to put in the footer area without changing anything. No need to put custom urls.
always links to the highest "root" domain.
is a not defined id tag that results in a link to the top of the actual page.
THE FULL CODE:
<a href="/" title="Back to the Home page"><b>HOME</b></a> | <a href="#" title="To the top of this page"><b>BACK TO TOP</b></a>
| BACK TO TOP
Put this in your site footer so it shows up on every page consistently, long or short, so it's something your visitors can count on. The Home link is useful because this is where most people would go after reaching the top navigation menu. Besides saving them some scrolling, you save them a click.