Problem with this bit. For one, FFXI reported ~500,000 players for several years in a row. Whether it's taken "at a certain point in the year", when it's that consistent year after year, it kinda indicates a trend.
Further, the Vana'diel Census was not purely a "marketing piece". It went far beyond providing population numbers. It provided detailed breakdowns of population by race, job, character style (hair, height, etc), home nation, and so on and so forth. It was several pages of all kinds of data provided for the players' consideration. It was more for the fans than for the public.I don't think I ever saw the Census mentioned on a general MMO news site. I always found out about it by going to the official site, or on a FFXI-specific fan site. That's not to say it wasn't mentioned on other sites. It just wasn't a high-importance, high-profile news piece.
Citing its overall population was just one piece of a much, much larger collection of data. I hardly think what race people played the most would be of much marketing value to them or the game.