MessageInspector not inspecting all requests?

Question

Here is the scenario... I have a service like this

public class Service : IServiceContract, IServiceBehavior
{
   public void ApplyDispatchBehavior(ServiceDescription serviceDescription, ServiceHostBase serviceHostBase)
   {
      foreach(ChannelDispatcher chDisp in serviceHostBase.ChannelDispatchers)
      {
        foreach(var epDisp in chDisp.Endpoints)
     {
           epDisp.DispatchRuntime.MessageInspectors.Add(new CustomInspector());
        }
     } 
  }
}

The problem is the message inspector does not fire AfterReceiveRequest or BeforeSendReply when hitting the service directy (http://localhost/Service.svc). I am wanting to do some customization of the html page returned(that lists the WSDL location).

The inspector fires as expected when calling any operations on the service, but not when accessing the service endpoint directly.

The web.config has the a single endpoint defined, basicHttpBinding. httpGetEnabled=true as well.