It's a powerful conceptual metaphor, to borrow a term from Lakoff and Johnson. Venkatesh Rao explains how metaphors structure our thinking about technology, and can hinder innovation:
As much as we focus on developing new technologies, it is also essential that we break free of certain metaphors that bind and restrict our thinking about what these technologies can ultimately achieve. The familiar “document” metaphor, among others, has cast a long shadow on how we think about the web, and is standing in the way of some innovation.
Consider these terms: page, scroll, file, folder, trash can, bookmark, inbox, email, desktop, library, archive and index. They are all part of the document metaphor, a superset of the “desktop” metaphor. Some elements, such as scroll, desktop and library pre-date the printing press, but all are based on some sort of “marks on paper-like material” reference.
I think you could add to this list a similar set of metaphors that have shaped social media, and in some ways limited it. Think of the use of the term "friend" or "follower," as applied by Facebook and Twitter, respectively. Facebook (and other social networking sites) have been accused of collapsing a wide variety of social connections into a flat category of "friend," making it hard to distinguish between people you're actively socializing with in the real world, people you were friendly with in high school but haven't seen in 25 years, people you don't really care about but don't want to offend, coworkers or superiors, and your family. "Followers" has a sound that I find alternately amusing and creepy, as if I were either a cult leader or target of stalkers.
Back to Rao:
It is important to understand that the document metaphor is more than a UI metaphor. It is in fact a fundamental way of understanding one domain in terms of another. For better or worse, we continue to understand the web in relation to how we understand documents. Unlike figurative metaphors, such as “he was a lion in battle,” which are simple rhetorical statements, conceptual metaphors (a notion introduced in the classic “Metaphors We Live By” by Lakoff and Johnson) like document-ness are pre-linguistic, and quietly ubiquitous. They infiltrate how we think about things on a much more basic level….
It is much easier to create technology that conforms to dominant metaphors. What we need to do as we enter the third decade of the web, however, is consider what we want the web to be rather than awkwardly fitting that vision into older descriptive paradigms.
Easier said than done, of course, but it's essential. Perhaps this is one of the reasons user co-creation or reinvention has become such a thing: users may be more likely to engage in this conceptual reframing than inventors and marketers, who spend a lot of time defining products.
Finally, it's worth noting that the whole industry of strategic marketing, as envisioned by people like Regis McKenna and Geoffrey Moore, was intended to define the conceptual metaphors in ways that would help people decide to buy products.