why does google cache mywebsite.com and not www.mywebsite.com ?

[Mattkau]

why does google cache mywebsite.com and not www.mywebsite.com ?

both sites work, however google is caching the non-www site, why ? does it make a difference?

[Mark Brian]

You should sign-up at Google Webmaster Tools, you can set whether you like www or no-www. It has a difference, so when link building choose only one.

[mlongley]

Originally Posted by Mattkau

why does google cache mywebsite.com and not www.mywebsite.com ?

both sites work, however google is caching the non-www site, why ? does it make a difference?

You can change that setting in google, and you should also change your .htaccess file to prevent that from happening... example make mywebsite.com, mywebsite.com/, mywebsite.com/index.html all default to www.mywebsite.com/.
This will prevent duplicate content and also it helps your backlinks to count all to the same page. Search engines will recognize www and non www as two different pages.

The rewrite will look something like:

RewriteEngine On
RewriteCond %{HTTP_HOST} ^example.com
RewriteRule (.*) http://www.example.com/$1 [R=301,L]

If you need help with redirects or .htaccess files.. you can always download htaccessible. It is a great free app for creating redirects on your servers .htaccess file.