I am not a web developer or a sys administrator, but I think the default domain should point to the same directory that the www subdomain points to.
The default is that example.com leads to your content and www.example.com forward to example.com. This is how it is done (according to http://no-www.org/ ):
RewriteEngine On RewriteCond %{HTTP_HOST} ^www\.(.+)$ [NC] RewriteRule ^(.*)$ http://%1/$1 [R=301,L]
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