Developer Priorities on bugs/exploits (Score 1)

In the beginning months of WoW the servers were brought down and "hotfixed" within days of finding "bugs" that allowed players to gain minor advantage over the environment. Contrast that to some "bugs" (driud shapeshifting breaking frost effects and "stun resist" powers not working, come to mind) that were known for over 6 months and not fixed. I was wondering if you could shed some light on how exactly you prioritize bugs/exploits and what leads to the decision to leave some bugs for 6 months and hotfix others in 2 days?