If I remember correctly one of the Fallout games had a Demo, as well as Daggerfall.
You remember correctly. However, the Daggerfall demo was just the intro dungeon where you end up after your shipwreck, and really was rather pointless as far as representing the complete game goes. I suppose they could've made a demo for Oblivion that ends where you get out of the jail, but that wouldn't give a very good idea of the complete game. If they made one for FO3 it'd just be the birthday party in the vault.