Plus, for a Linux user, you can already build such a system yourself quite trivially by getting an FTP account, mounting it locally with curlftpfs, and then using SVN or CVS on the mounted filesystem. From Windows or Mac, this FTP account could be accessed through built-in software.
Branches is one example! But really Dropbox is not a VCS.
Although some game studios do use Dropbox/Google Drive for versioning graphical assets - but not because it's a good tool for the purpose, they just don't have a better one.