g1smd - 7:24 am on Nov 7, 2012 (gmt 0)
What it does have is a physical existence on the server.
One of the most important bits of the server configuration is the ServerName or ServerAlias directive. It defines (in conjunction with the DNS settings on the DNS server) what hostname requests the server will respond to, instead of (err, in addition to) requests for a particular IP address.
Another important directive is the one that defines DocumentRoot. This defines the base folder of the server harddrive that will be web-accessible. Everything above that (the server OS, etc) will not be accessible from the web.
If DNS and servers didn't act the way they did, then rather than accessing a site using
http://www.example.com/folder/this-page you would be using
http://126.96.36.199/c:Documents and Settings/Users/Jim Doe/My Documents/Websites/Shop Web Site/May 2012 Version/folder/page.html to access the site and when Jim changes his PC out for a Mac, the entire folder structure "above the site" would be different.
We take this functionality for granted, but URLs are a reference system used out on the web and files are a separate reference system used inside the server. They are related merely by the action of the server software mapping URL requests to internal server locations. The server doesn't make URLs for files. The server responds to URL rquests by looking for particular files inside the server. A rewrite works "exactly backwards" to the way that most people seem to think about what is happening. A rewrite causes the server to look for a file that is not the default file suggested by the path part of the URL. Once you "get" that, you can do so much more with your site technical setup.
It's a comment that Jim used to post on a regular basis here. I'll readily admit that I didn't "get" it until at least the third reading.