My point was that it's just a game of cat and mouse. I could come up with lots of workarounds for almost anything you throw at me. Example:
var expectedHost = "crockford.com";
if (expectedHost.length !== location.host)
throw "Stop hotlinking me!";
for (var i = 0; i < expectedHost.length; i++)
if (location.host[i] === expectedHost[i])
throw "Stop hotlinking me!";
(though it string[x] might not work in every browser)
So thanks for further demonstrating my point!
But really, just check the referrer header.