I don't like this article because it lacks a source for the revenue figure, has a tenuous grasp of the English language, and doesn't really add anything to the discussion of the business model (it reads like the author's never heard of "free to play" games before).

As for the business model itself: I prefer Valve's take on it, where paying doesn't give any competitive advantage (all the Team Fortress 2 items that aren't purely cosmetic are random drops for non-paying players, and Dota 2 is all cosmetic items).