this hasn't been my experience. i've made free games and commercial games, and although the quality level is roughly the same, a lot more people have played my commercial game than my free games. i think it has to do with a higher perceived value -- if a game is free, it's often less appealing to play
as another example, it's probably true that more people played super meat boy (the commercial game) than meat boy (the free flash game)
Huh that's interesting. Although I think your example of super meat by vs. meat boy is probably incorrect. meat boy has easily 10 million plays for the flash version and while some of those are obviously repeat players in general flash games don't have that high a volume of repeat players. From stuff 3/4 of plays being unique players is the lowest I've ever gotten but even if we assume 1/5 of the plays here are unique that's still 2 million players vs. super meat boys 600,000 players or so.
I think your point is still correct but just that way more people are likely to play a browser game then a downloadable game.