It's kinda like dating (although I haven't dated in 10 years, since I met my wife).
You need an initial attraction; but you know that there's something about her, or him, after the first few dates that suggests you'll be together for a while.
I've dated women who were a bit more flashy, wore a bit more make-up and were in some cases prettier, but I didn't feel that connection, or substance behind that connection, like I do with my wife...
Yes, my wife is ARR.
Seriously though, I think ARR will be initially widely successful but like most MMOs people will get bored, or not appreciate the atmosphere in ARR the way fans might.
If updates, patches and content is added at a good pace, if Yoshi can keep up his level of enthusiasm for a few more years (I don't see how this is possible and actually see him resigning within a year or two because of stress) then ARR will have a pretty large sub base (not record breaking) for a while.