There's No Such Thing as a Web Site
I never thought of it this way, but of course Tim Bray is right in saying that There's No Such Thing as a Web Site: "The technology that makes the Web go doesn't have any built-in notion of a "site" or a "home page", even though that's how people think about things."
Here's his follow-up post, in which he is proposing a new HTTP "Website:" header.