I think what people forget is that the game released on the 13th of November, and the study (released 1/23) encompasses anyone who picked up the game within 10 days of launch.

This means that the 60+ days category is actually the *smallest* window of any of the categories, averaging 5 days. Someone who picked up WotLK on the 10th day after launch literally had 1 day to fall into the 60+ category.

It's no surprise then that the 60+ category is so minuscule.