No, WoW has expanded to its player base beyond WarCraft and Diablo, but not to the mainstream. Many of these subscribers will not play another MMO in the near future. MMOs need to expand their playstyle from treadmills to focusing on fun factor. Mainstream players do not have the time or see any benefit in investing hours upon hours into an avatar that exists in a static treadmill world. Technology also needs to progress to allow MMOs to play like standard games, many mainstream people will not be willing to deal with the technical issues MMOs typically have.
-Patrick Lister, Computer Sciences Corporation.