Do you know what URL rewriting does? Have you seen it in action? If so, you should be in a good position to speculate how it works. Why don't you describe to us how you think it might work, and we'll comment on your answer.
Ping & DNS - updated with new look and Ping home screen widget
URL Rewriting is basically a mechanism of preserving session in case the browser is not cookie enabled. Here, the URLs are always appended with the sessionId so that the client can always send back this seesionId to the server. In case cookies are supported by the browser, then the sessionId is sent as a cookie and URL rewriting is not required.