lol, I remember when WoW came out, all of my friends wanted me to try it. I've beaten off playing that game since. I can't honestly see myself promoting it through a card combo purchase.
Well, I can't really say why it's such a popular game, probably because of it's complexity and attention to the characters. I mean, I've played GW , FFXI and soon ragnorak online and the short comings for GW are made up in FFXI, better diverse armor, items, ontop of a higher level cap, the things that are lacking in FFXI are made up in GW, no party grinding and unique weapons are pretty easy to find.
WoW takes both GW and FFXI mechanics to different venues, WoW came out, maybe a year after FFXI? And short of the terrible graphics on both, WoW has a lot more 'to do', FFXI is really hard in some aspects. A friend of mine jokingly said, asians enjoy level grinding and hate the melee class which is why casters of any kind have uber abilities that borderline ridiculous.