Whilst index.htm or default.htm are the rule of thumb, they're not the only files that can be served by default. It's up to the administrator of the web server as to what files can be used as default files, and in what order they should be used. Other common ones include index.html, default.html, index.php, index.asp and index.asp. Basically anything goes... on this site files with a .go extension are defined as being scripts (I reckon PHP or ASP) and the default seems to be a file called home.go