The site's name, perldoc.perl.org, doesn't appear anywhere in the mark-up for the page. For sighted users with CSS and images enabled the name is visible baked into the background image on #header.
But users using a speech browser don't get told what the site's name is. Nor do those on slow data connections, people running lynx on a server without X installed, and search engine robots.
The best fix would be to put the text “perldoc.perl.org” inside the (currently empty) <a> element inside #homepage_link, then use CSS to style the text as desired.
If it's desired to keep the site name text as an image then an alternative would be to put it as an <img> element inside that <a>, with alt=perldoc.perl.org.
In either case header.png would need the baked-in name removing.