Varies a lot in the lore. Some accounts like Urzura, Daughter of Urthemiel, talks of the raising of small army (albeit of militiamen) to corner the High Dragon in her lair and slay her. On the other hand the Pentaghast family, the rulers of Nevarra and family of Cassandra, are renowned as being Dragon Slayers and it only mentions the family and doesn't detail the raising of any armies to hunt the beasts. Hell, we even see Cassandra kill a Drake and a High Dragon in Dawn of the Seeker (if I recall correctly, been a while since I saw it).
I suppose its all a matter of circumstances, even within the Lore. DA:I seems to lending more credence to the tall tails by making the Dragon battle tougher and, if I saw it correctly in the trailers, made it so that dragon can actually flee battles making it harder to pin them down and kill them in one encounter.
-D-