Por que isso não funciona?

Rota:

<code>routes.MapRoute(
                "Summary",
                "{controller}/{id}",
                new { controller = "Summary", action = "Default" }
            );
</code>

Controlador:

<code>public class SummaryController : Controller
    {
        public ActionResult Default(int id)
        {
            Summary summary = GetSummaryById(id);

            return View("Summary", summary);
        }
    }
</code>

URL:

<code>http://localhost:40353/Summary/107
</code>

Erro:

<code>Server Error in '/' Application.

    The resource cannot be found.

    Description: HTTP 404. The resource you are looking for (or one of its dependencies) could have been removed, had its name changed, or is temporarily unavailable.  Please review the following URL and make sure that it is spelled correctly. 

    Requested URL: /Summary/107

    Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.225
</code>

Atualizar:

Deixe-me atualizar a questão com uma pergunta mais inteligente. Como posso ter os dois?

<code>routes.MapRoute(
                    "Home",
                    "{controller}",
                    new { controller = "Home", action = "Default" }
                );

routes.MapRoute(
                    "Summary",
                    "{controller}/{id}",
                    new { controller = "Summary", action = "Default" }
                );
</code>