You are probably only receiving HALF your allowable page rank due to a bug in how search engines view URLs. Google and most other search engines see your-domain.com.au and www.your-domain.com.au as two completely different domains. The only difference between the two is that the www is missing off the first one. They both go to the same page on the same website. They both give exactly the same results. Why then does Google and others count them as two different sites and therefore spit your page rank between them.
It has something to do with Canonical links – meaning the process of chosing the best available link when more than one is available.
Matt Cutts from Google explains:
* www.example.com.au
* example.com.au/
* www.example.com.au/index.html
* example.com.au/home.asp
“Technically all of the above urls are different. When Google “canonicalizes” a url, we try to pick the url that seems like the best representative from that set.”
What can I do to protect my valuable page rank?
The answer is simple if you are on an Apache web server (Linux hosting). The answer is Mod-Rewrites.
Add this code into a .htaccess file (a simple text doc with the file name .htaccess) and drop it into your ROOT folder.
RewriteEngine On
RewriteCond %{HTTP_HOST} !^www..*
RewriteCond %{HTTP_HOST} !^$
RewriteCond %{HTTP_HOST} ^([^.]*).(com.au|com.au/)
RewriteRule ^.*$ www.%1.%2%{REQUEST_URI} [R=301,L]
Now, when your server detects a request for a page and it has not got the www. in the URL it will automatically be added in there. That means that Google will always contribute any Page Rank to the one URL and it will no longer split the Page Rank between the two URLs.
For more info read the manual here at Apache (http://httpd.apache.org/docs/1.3/mod/mod_rewrite.html).