There are about 300k games played per week just on FICS. There are a few hundred USCF games played each week just in Louisville KY (where I play). I would imagine if you managed to pull from all of the sources, 600k wouldn't even amount to a day's worth of games.
The set the author used suffers greatly from selection bias. Games are usually only included in commercial databases because they're interesting, or were played by interesting people. So I'm not sure anything interesting can be drawn from his results.
Also, there needs to be some control put in place to account for rating differences. The Eli system isn't that old, and in the past players with drastically different levels of skill were more likely to play each other.