Deploying Web Forms Application Using Routing On IIS 6?

To clarify, the scenarios I am looking at involve deploying ASP.NET 4 Web Forms application that employ RouteTable.Routes.MapPageRoute:

public class Global : System.Web.HttpApplication
{
public static void RegisterRoutes(RouteCollection routes)
{
RouteTable.Routes.MapPageRoute("questionnaires", "questionnaires", "~/Pages/Questionnaires/List.aspx", false);

[Code]....


Scenario 1: The application is NOT hosted as a virtual directory in an existing website, but is a stand-alone website (it is its own starting point). It has its own application pool. When deployed, it worked without any tinkering.

Scenario 2: The application is hosted as a virtual directory underneath an existing website. It also has its own application pool. However, I received 404 errors when trying to access the routes I had mapped out. Fortunately, I had experience getting MVC to work in 3.5 sp 1, so I tried that method: opened the properties dialog of the virtual director, went to the "Directory" tab, click the "Configuration" button, and added a Wildcard application map to the aspnet_isapi.dll and unchecked the "Verify that file exists" checkbox. This made it work.

My question is why did I have to add a wildcard application map in the second scenario but not the first? If it helps, the root website that hosts the virtual directory in the second scenario is set up with ASP.NET version 2.0.50727.