Just realized - if you're a casual gamer, ideally....

[Naqaj]

I thought WoW was casual and the "new" FFXI was casual.

Which both have fairly large populations.

...

6 years ago, WoW increased the MMO playerbase 100fold simply by making the game more accessible then the competition.
F2P is basically doing exactly the same, removing yet another barrier of entry, though this time by means of affordability, not game design.
Console MMOs are removing the barrier of hardware complexity, though as the first attempts have shown, this makes it neccessary to adjust the basic game design to accomodate for the simpler controls. Once they get that nailed down, there's a huge untapped market to get into.