Well, it's not a given they'll play the song, and they could play it elsewhere in the set. And coming off two sets one of which is an 80 minutes long album, it makes more sense and balance to have a single song, maybe an epic, as encore. But just imagine how cool it would be for people sitting over the Finally Free outro thinking "yeah, we all know it" and then the static goes on and on and you hear the little bell and FFFFFUUUUUUUUU!!!!!!!