Areas in the original World Of Warcraft were faked through visual tricks, according to Blizzard.
Lead systems designer Greg Street said that a lot of work was required to update Azeroth for flying mounts because it used graphical tricks that only worked from the ground.
"You don't really realise it when you're walking around, but much of the original world was faked in interesting ways," he said.
"Like Hollywood front pieces that look great from the ground and it looks really cool, but the moment you peel back the curtain and fly up in the air, it's like 'ugh, that's terrible, that's crazy!' It took a lot of work to get all of that straightened out.
"Particularly for the cities, Stormwind and Olamar were never designed to be seen from the air. In an internal build if you were to levitate up, all of a sudden things would turn invisible and drop away."
Street said that the team took shortcuts to smooth out load times and to ship the game quicker.