Not sure about about why Portal is number 1. Good game, innovative, but Half Life 2 is far superior in every way. Also, Wind Waker above Link to the Past and Ocarina of Time? Honestly Bioshock and Mass Effect 2 should probably be higher, as well as something like Doom or Goldeneye 007, since FPS games are the biggest genre and they made it what it is. But, I'm not sure if innovation and legacy are put as high in their minds as in mine.
However, I agree World of Warcraft should be up there as it is an incredible feat of technology, innovation, and video gaming. When it came out it was absolutely mystifying and it is the only game I have ever played year-round for coming up on a Decade. It is easily deserving to be in the top 10 with some of the greats.