I'd take the total opposite point of view.
The RPG / general game aspect of it makes WoW much more interesting to me then Second Life. The latter I would say seems like a pointless time sink. I look at it and think "whats the point? Whats my objective in spending time playing this 'game'?" and the only answer I can come up with is to be a capitalist whore (to put it very bluntly). I'm sure for some people going into a game to make friends and profit is a great idea. For me though, I'd much rather overcome the various challenges in WoW and progress to being a better skilled and equipped player. The most fun I've gotten out of WoW is all the raiding once I actually hit 70. Very interesting story, and very original boss fights requiring a team of 10-25 people to develop extensive team work and fulfill very certain roles.