I think that one of the most basic ways in which a Google doc can operate in a collaborative setting is that it enables other to make changes to it.  When a Google doc is started by one person, it can be instantly shared with others, enabling them to be able to edit and change it.  When the document is shared with others, they become instant collaborators.  This is how a Google Doc can be a collaborative effort.  Changes and alterations are instantly saved every ten seconds and since that there is only one document with multiple collaborators, changes are saved and there is little chance of losing the collaborative work.  As long as collaborators have a google domain account, they are able to use the document in a collaborative manner.  Emails are not needed for it and the original document is shared, so the need to merge changes is not required in order for collaborative work to happen:

Another advantage is that multiple users can make edits to the same files at the same time. This is called online collaboration, and it could streamline teamwork over the Web. Because Google Docs preserves earlier versions of documents, there's no reason to worry about irrevocably changing a file. Collaborating on files might mean changing the way we think about document management.

Through this, there is a sense of collaboration and a sense of being able to use Google Docs in a collaborative setting with others.