How to dispose IHttpModule correctly?

All implementation of IHttpModule I've seen looks following:

class HttpCompressionModule : IHttpModule
{
  public void Init(HttpApplication application)
  {
    application.SomeEvent += OnSomeEvent;
  }

  private void OnSomeEvent(Object source, EventArgs e)
  {
    // ...
  }

  public void Dispose() 
  {
    // nothing here !!!
  } 
}

I am wondering why is the Dispose method always empty? Shouldn't we unsubscribe the event which we subscribe in the Init method?