This is only mildly related, but I remember reading somewhere that the dragons themselves perform random activities and aren't always there to attack you.

Best example of this: I did read that some of the dragons aren't meant to attack you, but just to investigate what you're up to on behalf of the Bane of Kings. One time, when exitting Solitude I had one -plain- dragon follow me all the way to Dragon Bridge and beyond before just roaring off in to the mountains.