Man that data seems wrong.
"Though small--numbering around 3.8 million [heavy gamers] ...buy 4.5 games each month."
Granted they are buying games for PC and multiple console platforms, that is about 54 games bought per year. Are there 54 different games released each year?
For the sake of argument, let's say that there are 54 games release each year. That means that every one of those games sold around 3.8 million units, which would be staggering. The number goes down ONLY if MORE than 54 games are released each year. That all seems highly improbable.