Dedicated to those people who insist that http://www.example.com and http://example.com must point to the same thing. Like I’ve said before, they are not the same thing, they are supposed to be equal only in the eyes of the inexperienced, and yes they are one more place for configuration errors (and user confusion) to emerge. Example (valid as of 2011/07/02 12:24):
Directory Listing Denied
This Virtual Directory does not allow contents to be listed.
Managing organized complexity 
according to your theory, there is nothing wrong with that example, unless the http://example.com was advertised somewhere. I mean, http://www.example.com and http://example.com in this case do return different results, just like you say that they should :-)
Now, I maybe inexperienced but it is my opinion that both http://www.example.com and http://example.com should be configured. www is vestigial, the equivalent of tailbone (coccyx) in my book.
best regards.
Yes they return different results and yes one could argue that even the wrong one is “configured”. The user suffers anyway. And the user suffers because of the introduction of helpful perceptions like http://www.example.com being equal to example.com and helpful browsers that prepend www. to example.com.
Decades have passed. We must decide on one consistent interface.
I wonder what will happen when someone registers http://www.www. Then we can discuss http://www.www.www versus http://www.www.
Nah, this kind of discussions is for pundits and pedantics like me. They serve as the countermeasure to entropy.