He says:
"Either IIS URL rewriting or ASP.NET routing can be used to implement URL manipulation scenarios for your Web application. ASP.NET routing is a solution that is optimized for ASP.NET, thus it may be preferable for Web developers who design their ASP.NET applications from the ground up and want to have a clean URL structure. IIS URL rewriting is a generic URL manipulation mechanism that addresses a multitude of scenarios. In particular, it can be used by Web developers as well as Web server/site administrators to enable clean URLs for existing Web applications without modifying the application code."