Sure, but at the same time - sometimes people don't return. Yoshi P asking people not to retire from the game shows that Square Enix is afraid of the churn rate of their customer base. Sure, not everyone has to be subscribed, but the more people are subscribed the better, its calculatable revenue which is worth much more than single time purchases, and helps cover operative cost of an MMO project. That is the point people are trying to make here. More money is the goal of every company.
Or, inTwintaniaTitania words: "Bigger is Better".