Oblivion observation

I was playing a little Oblivion last night and was just roaming around an old abandoned fort.  After clearing it out of Trolls (not easy, btw) I was ready to go back to town, so I ran back to the exit.  Somehow, there were (2) Trolls by the exit, so I just ran by them thinking they would just stay put.  They didn't.  They followed me out into the open and chased me down the common road.  I was faster, so I kept them from gaining on me but just barely.  So I kept turning around to see if they would give up (like in other games I play) and they DIDN'T.  I was determined to take them all the way back to Imperial City if necessary, but they started landing blows.  I was getting nervous.  Then, I saw an Imperial Guard on horseback patrolling the roads, and I thought SURELY the game isn't smart enough to have that now NPC engage in our melee.  I was wrong AGAIN.  He dismounted and engaged them both with his silver longsword and I ran for cover and drew my bow.  I helped where I could, but he dispatched one and then fell to the other.  I finished off the remaining Troll who was severely wounded with a few arrows and a weak fireball to stop them from regenerating.  I was then able to collect the Imperial armor/weapons and headed back to town.  It was an amazing experience and one that made me like the game very much.  Looking forward to crossing monsters with NPC's again.  I love doing that...