I think you may be thinking of a different VCS such as SVN as Git actually just stores the meta data (changes/deltas) and not full versions of the file in each commit.

As an example when you clone a repository, it downloaded it, then in goes through a process of 'Resolving Deltas'. This is it going through the history applying the changes/deltas to the files so that they are up to the most recent revision.

The only files that are added in full are binary files.

Some reading: http://git-scm.com/book/en/Git-Internals-Packfiles :)