You are not going to get that icon unless you have an Apple TV second generation and it is on and on the same network. There is no point to displaying the icon if you don't have something with which to use it.
Of course if you did have an ATV you could already access your iTunes content on it. So if your iPad is getting its video content via iTunes it can be pointless to then use the iPad to stream to ATV. My iPad only has a small subset of what is in my iTunes library so I rarely need to to stream from the iPad.