Well, one thing that definitely contributed was that Blizzard had already established the scene for with Warcraft III, so people sort of knew what type of world

Well, one thing that definitely contributed was that Blizzard had already established the scene for with Warcraft III, so people sort of knew what type of world to expect. Also, Blizzard's other games (Starcraft and Warcraft mainly) were a huge success, so that gave WoW more credibility.