That list always confused me since games on it appeared and disappeared so randomly so I checked out how it worked.
The way it works is every registered person can place a hype score from 1 to 10 on a game and the game with the highest average ends up on the top, currently xsyon has 300 votes compared to TOR and GW2 which has 3,5k and 2k respectively. So it's relatively pretty easy to influence the score either way for xsyon atm.
Took about 15 sec to go to mmorpg.com, click #3 spot, Xsyon, click hype up top, move the slider, and put in a comment. Great work everyone... let's keep it moving!!