They had to deal with it because Blizzard overlooked that problem. Blizzard realized it was a problem in TBC and then they implemented it. Why shouldn't it be implemented on Nostalrius just because Blizzard didn't think about it befor?
http://www.blizzardguides.com/burning-c ... guide.html"The big news though is that Blizzard has introduced new dynamic spawn rates for Outlands that changes the spawn rate for a Monster based on how many people are in the immediate mini-zone. So when there are 493 people camping the same named quest mob in Hellfire Peninsula on Jan 16, there will be an almost instantaneous respawn of the mob when it dies. "