In the latter half of the twentieth century, a true heavyweight of an academic named Clifford Geertz was pouring out docs on human behavior. His guiding thesis seems to have been that human behavior is a result of human interpretations of symbols of meaning within the groups they inhabit.
I was introduced to Geertz's work via his groundbreaking Religion As A Cultural System, in which he defines religion as:
(1) a system of symbols which acts to (2) establish powerful, pervasive, and long-lasting moods and motivations in men by (3) formulating conceptions of a general order of existence and (4) clothing these conceptions with such an aura of factuality that (5) the moods and motivations seem uniquely realistic.
Number 1 and number 2 are more or less Geertz's definition of a cultural system.
Let's exchange existence for "what we do with our time" and you get pretty close to the ways we spend our free time online--gaming being one of them.
And now let's put _games_ behind specifically, and talk about cultural systems instead, and how A Marketplace As A Cultural System works.